Bad Fraps Lag Wile Recording?

When i play games like say.. TF2 or suchs Source mods and games i usually get 100+ FPS but when i try to record with fraps even at 30 fps and half size with the games graphics down and resolution down i get REALLY bad lag.. :| like goes from 30 to 1 and seizures around 10 fps :( what things change how fraps works? hard drive? graphics card? ram? i have a 360gb hard drive, ATI Radeon HD 4670 graphics card, and 4 GB of Ram..