I have a problem . .

hi , i try to record my gameplay with fraps but it's impossible because my PC lag very hard and my caracter when i play can't move . .it's all blocked.
This is my tecnical information of my pc:
2 gb ram
Windows xp
NVIDIA GeForce FX 5500
80 gb hard disk ( only 20,3 gb in use )
what must i do for record with fraps wothout lagging?
tnx