Most performance loss might be suffered due to 'bad' drivers. Remember, latest drivers doesn't mean they are best.
You might want to look 3dguru.com forums or similar sites for more detailed info.
There might be many bottlenecks, poor motherboard, HDD, system and bios setup and many others too.
Just to compare
stock E6600
1gb ram
8600GT
7200 RPM 160GB HDD
1680*1080 fraps recording without AA and AF in game at max details had stable 30 FPS+
Win XP 32bit and good drivers.
and my home PC
Athlon 2500+@262x11 (2772mhz) running 2x 512MB 2-2-2-11-1T fsb/ram ratio 1:1
GF4Ti 64MB
7200 RPM 80GB HDD
Win XP 32bit
1024*768 in game (But i think fraps was cuting to 800*600), lowest details , no AF/AA stable 20 FPS+
On above PC happened to me to record thaddius with 3-4 FPS during whole encounter becouse i've been using best available counter-strike drivers for GF4Ti. Havent had problems with playing though
