One of the nice things about Linux is that most drivers come with the install set, un-like windows when your done with the install, now you have to go to all the card manufacturers to get the updated drivers. I have been running ATI cards for a long time, my first was an ISA card (and it was bleeding edge at the time). You did not list your sound card, what is it? If SoundBlaster the drivers are there. Next would be network card, did not see it listed in your post, but most standard cards are supported.
The reason I said you might be disappointed if you play othe games, is that there are not linux versions of the games. Dungeon Siege for example, is a MicroSoft game, and I can’t see them ever porting or allowing someone else to port to linux. A program must be coded and complied for the OS for it to be able to run on the OS. Now there are windows emulators, WINE being a prime example, but the problem with emulators is that what you have is your native OS, in this case Linux, which runs you emulator (another program), which then runs the program. So in most cases you will not get the performance that you would by just running windows nativly. Because you are creating a dual boot system, your better off running native windows programs from your windows boot.
With the exception of using WINE as above, you will not be able to run your windows programs, like MS Office, but, the Linux distribution, Mandrake in this case will offer you many optional programs to replace your windows apps (openoffice for example will provide most of the functionality of MS Office and ever read and write to natvie format that can then be opened by MS Office) and are included in the distribution.
Mandrake is not the only Linux distribution, someone else mentioned Slackware, I have not run it sence the mid 90’s so I will not comment on the state of the distribution, many people run it and swear by it, but I can not comment on it at this time. Most of my machines run debian in one form or another, but I would not suggest it to a linux noob (in this case I don’t mean noob in a bad way). There are many others, but again without running them personally, I refuse to comment on them. One of the biggest complaints about Mandrake by linux people, is that it looks too much like windows, but in this case, with you being new to linux and knowing windows, I think it would have the lesser learning curve.
You can download the Mandrake iso images and burn your own CDs (although you did not list a burner in your specs), but unless you have a broadband connection, I would suggest you find a boxed set.
Oh, one more thing, BACK UP YOUR HARD DRIVE BEFORE YOU START!!!
I know I have said this already, but I can’t say it enough, so BACK UP YOUR HARD DRIVE BEFORE YOU START :bump: