Answer in First Part

System Title

All editions are known as Warhammer Fantasy Roleplay. The first edition, hereafter 1E, is often seen using a separator is logos for "Role•Play". Online resources will often make the distinction for you with numerical notations.

Online 1E CharGen and resources

While I'm unsure of online 1E character generators, 1E was released in 1986 and rereleased by Hogshead at the very cusp of online resources like the WWW, they may be tough to find, and when found, horribly written by today's web standards.

Consider joining the Strike-to-Stun forums for 1E if seeking a deeper availability of resources.

Also, MadAlfred's WFRP Pages contains some of the richest resources for 1E still online (including two 1E conversions of Druidic and Elemental magic for 2E.)

Answer in Second Part

WFRP 2E, or second edition, was released, in 2005. It is almost fully compatible with 1E with the following distinctions:

Character Builds

Gone is the 1E assumed compatibility with Warhammer Fantasy Battle. All stats are computed on a percentile system. However, the compatibility between 1E and 2E is an easily managed task.

Other mechanical changes address odd "munchkin" builds of dwarf PCs, e.g., the aforementioned "Naked Dwarf" problem.

Career Changes

The central feature of WFRP 1E, the Career System, largely remains intact in 2E, except in Magical (Arcane) and Clerical (Divine) career paths...

Magic System Overhaul

Gone are is the tiered levels of arcane and divine magic careers. These careers are aligned mechanically with all other careers in the system.

The new magic system use the unified target number mechanic, ties well with the skill and talent system throughout, provides for dramatic grim failure, and reagents.

Canon Changes

1E is set during a rising tide of Chaos incursions and plots by Ruinous Powers. Ostensibly, 2E is set following the Storm of Chaos, a Warhammer world event that was played out around the world by Warhammer Fantasy Battle players, that also dovetails with the conclusion of original The Enemy Within campaign.

Conversion from 1E to 2E resources

Finally, Liber Fanatica has rich, downloadable conversion and support information for 1E-to-2E conversion. LF's Volume 1, The Character Compendium was compiled by play-testers of 2E and contains details on converting your 1E PCs to 2E.

These conversion tools would be very helpful if you wanted to say chargen using the 1E ruleset on hand and purchase 2E material at a later date.

Availibility of WFRP 2E

Almost all 2E material is now available for purchase at DriveThru RPG as PDF (and some titles as Print-on-Demand).

Hope this helps... 1E resources are out there, but show their age (if not in web design alone; remember 1E was released in 1986 and Al Gore didn't invent the internet until at least 1992--at least that's when he co-sponsored public access to ARPANET in the US Congress).

I've never encountered a character generator that wasn't hit by a "Cease & Desist" letter from GW. All of the ones I've seen have been removed from the net.

In general, all you need to look at is the publisher. If it was Games Workshop, Citadel, Hogshead Productions, or Warpstone Magazine (to issue 22), it's for 1E.

If the publisher is Black Industries or Fantasy Flight Games, it's not for 1E.

WFRP 2E setting materials can be converted with only minor difficulties, but character and monster conversions may result in some odd issues.

WFRP 3E materials are mechanically totally incompatible

Easy: 9-20.

Let's start by disproving that 11-20 is the highest threat range possible in D&D 3.0/3.5.

Take the Improved Critical feat, which doubles your threat range. Also take Disciple of Dispater (Book of Vile Darkness, 3.0) up to 8th level, which triples it. These abilities explicitly stack. D&D multiplication rules turn this into a quadruple modifier.

Use a weapon (which must be iron or steel for DoD to work) with a natural 18-20 threat range. Quadrupled, that's 9-20 from one 3.0 book and the Player's Handbook.

Combining 3.0 sources: 7-20 or even 1-20?

Sticking with 3.0, we have the Weapon Master class (Sword and Fist). Its 7th level Ki Critical ability increases a weapon's threat range by +2. If this stacks multiplicatively with DoD (which it probably does), we have (3+2)*4 = full 1-20 crit range. If it stacks additively with DoD, we have a comparatively unimpressive 7-20.

Answering the question of whether it's possible to get both DoD and WM to the required levels pre-epic in 3.0 is left as an exercise to the reader.

There is also the 3.0 Stump Knife (also Sword and Fist), which has an interesting property:

Against foest to whom you have dealt damage during the course of a continuous melee, the stump knife's critical range is doubled (17-20).

So for the small price of losing a limb, we can increase the multiplier to x5.

3.5 and 3.0 together: Very hard to tell.

3.5 did lots to nix the range-stacking that was rather popular in 3.0. Muddying the waters are changed critical stacking rules, how those interact with DoD, and whether the Exotic Weapon Master from Complete Warrior counts as an update to the 3.0 Weapon Master.

One specifically 3.5 crit-enhancer is the 7th level of Streetfighter Barbarian, which grants a +1 to your threat range when charging.

Honorable mentions: Things that don't apply

Taking up to the 7th level of Psychic Weapon Master (3.5) is frequently mentioned. This doesn't actually work with DoD, as PWM works with crystal weapons and DoD with weapons of metal. (The Aptitude weapon enhancement from Tome of Battle also doesn't work, as that one applies to feats rather than class features.)

Serrated weapons are also frequently mentioned in discussions (increase threat range by +1). These are 3rd party additions, not from D&D books. Chainblades (a native 17-20 range) fall in the same boat.