The easy way to do it would be to use Steam's backup feature. Select "Steam" on the menu bar, then "Backup and Restore Games...". Choose "Backup currently installed games", after which you can pick TF2 then point the backup utility at your thumbdrive to save. (It tells me it will be 6999 MB, which suggests that it compresses the backup, which may also be why some said it takes longer than just copying.) To install on other computers—restore—go to the same menu item and just pick "Restore a previous backup"
You could also just copy the team fortress 2 *.gcf (and probably the source *.gcf, and maybe the half-life 2 *.gcf's...) files out of the \steamapps folder and put them on to the computer where you want to "install" the game.
Other online sources, such as the Valve Forums, have specified these files as being the core ones:
multiplayer ob binaries.gcf
orangebox media.gcf
source 2007 binaries 2.gcf
source 2007 binaries.gcf
source 2007 shared materials.gcf
source 2007 shared models.gcf
source 2007 shared sounds.gcf
source engine.gcf
source materials.gcf
source models.gcf
source sounds.gcf
team fortress 2 client content.gcf
team fortress 2 content.gcf
team fortress 2 materials.gcf
Total size: ~11.0 GB
The files in /steamapps/[username]/team fortress 2 are reported to be 'personal' stuff, screenshots (prior to a recent update), keybindings, crash reports, etc.
You could actually copy the entire /steamapps folder, or at least all the *.gcf and *.ncf's Unless you're hard-pressed for time, I'd just use the backup/restore, as it's all but guaranteed to work.
You can use Steam Family Sharing to use two accounts (and, therefore, two profiles) on one computer. You need to have family sharing (currently in closed beta) enabled for the account that owns MW3. Enable sharing for the computer you want to use, install MW3 and then your brother can login and play with his own profile on that computer.
Family Sharing, however, only allows one user to be playing at any given time, no matter the game. Your brother will be kicked out of his game within 5 minutes if you launch any game in your Steam library.
Best Answer
If you want to play on the same PC:
Yes. Steam should recognise that the game is already installed. Failing that (which definitely works on games newer to Steam, but I'm unsure about older games like TF2), copy the contents of your SteamApps folder to his. (see the SteamApps\username instructions below)
If you want to play on seperate PCs:
Yes. Open your SteamApps folder. This will be depend on your operating system and be:
for 32 bit (older) Windows systems,
for 64 bit (newer) Windows systems, and
for Mac OS X systems.
You will need to copy all files who's name begins with "source" or "team fortress 2" from that folder on your PC to the folder on your brother's PC. There is also a file called
winui.gcfwhich you will need to copy in there also.Then follow the instructions in the below heading.
SteamApps\usernamefolder instructionsYou will also need to copy the
<your steam username>\team fortress 2folder inside your SteamApps folder toSteamApps\<your brothers steam username>\team fortress 2. If there are any folders beginning withsourceorwinuiin there as well, you should copy those also. Apart from required files for the game itself, these folders contain configuration and downloaded maps.Notes
If you miss any individual files then they will be downloaded when Steam launches the game.
These instructions will not work for Windows to Mac, or Mac to Windows.