At first: It would be nice if you added a more details error description (error message? servers listed or not? timeout at connection to the server? etc.).
Depending on you country you'll the CUT or the UNCUT version of the game by Steam. CUT and UNCUT version are incompatible (at least at the time i played); so you can't play with a CUT version on an UNCUT server and vice versa. There will be probable no servers left for the UNCUT version. There are patches out there to convert a CUT version to UNCUT (just google for "rainbox 6 vegas 2 uncut patch").
Another widespread problem is that some routers require configuration. You have to open these ports;
TCP: 3074 to 3174 + 10130 (in- and outgoing)
UDP: 10140 (in- and outgoing)
I know of only one way that this can happen in windows, and has nothing to do with Steam other than their not-so-great decision to install all content into Program Files.
If you are on Windows 7 or Windows Vista, and you have UAC set to ON, then change it later to OFF, this can happen.
UAC does thing evil thing where if a program tries to write to a "protected" area like Program Files, EVEN IF YOU ARE ADMINISTRATOR, when you get a UAC prompt and give permission, it actually writes any files that would normally go into that directory into a "virtualized" directory somewhere else.
If you turn off UAC, that will no longer happen, and as an awesome bonus, it will no longer know about the files that it virtualized.
So in your case, if you had UAC on, installed a ton of games, then later got sick of UAC and turned it off, this would happen as you described.
See the second paragraph in "Features" in the article on User Account Control.
If you have done this and turn on UAC again, your content will come back, but be a TOTAL mess because if you've downloaded more stuff with UAC off, then that will be invisible when you turn UAC on, and vice versa.
this drove me a little crazy once before I realized what was happening.
i'm curious to know if this is your issue.
Best Answer
What exactly do you mean by
not compatible with the normal version? The Steam version can play online with the standalone version normally.PunkBuster did give me some trouble because of the Steam Community In-Game. Since it draws itself on top of the game PunkBuster thinks it's a cheat. I had to disable the overlay in order to play. See this topic in the Steam forums for more information on that issue.
You have to create a BF2 account in order to play online. You can play with it in any version of the game, be it Steam, standalone, your friends's copy...
You will receive a CD-Key, even if you buy it on Steam. You have to be signed in Steam in order to play the its version of the game, but you could theoretically borrow the standalone version from your friend and use your key with it.
Also, with the Steam version you don't have to worry about keeping your BF2 DVD in the drive, since it's not required.