games really don't take up much space on the computer, especially if you know how to maintain it. i'll talk about my computer and give a little advice:
- i have 2 partitions: a larger main one, running on Win2k English, and a smaller backup partition running on WinXP Chinese. trust me, dual-OS helps, i remember half a year ago when i deleted some dll's on Win2k by accident and couldn't boot at all. luckily for me, having a second OS allowed me to back up my stuff on CDs before formatting the computer.
- i've used up about 8 GB out of 25 GB on my main partition so far. even for a big-time gamer like me, my games only take up 3.5 GB. (my entire HD is 40 GB)
- if you have limited RAM like me, maximize its efficiency! i have 256 MB RAM (trust me, this isn't a lot for a gamer). disable all the task bar icons (the ones on the bottom right) you don't need.
- download Ad-Aware from download.com and scan your HD and RAM with it. trust me, this helps. the first time you run it, you'll never expect how much spyware and crap is clogging up your HD and memory.
- run a virus scan on your computer once in a while (i do it once a week), or better yet, set scheduled scans. make sure the scan pattern is constantly updated tho.
- clean up the HD! depending on how large your HD is, if you have so little space left, chances are you don't need two thirds of the crap on it! decide what you don't need, and delete the stuff (don't just delete to Recycle Bin, delete the stuff altogether!)
- if nothing works, i'm afraid formatting is necessary.
hope that helps.