Welcome sean2002!!
Same as toft-dk, I play Q3 and UT with the seti CLI running in background on my XP 1600+. Only an occasional, very slight hiccup in games, nothing disruptive. My machine is always on 24/7, last reboot 3 days ago was caused by temp monitoring proggie locking up......
Some have had trouble using Outlook 2000(?) and the CLI.......