PLEASE HELP ME!!! gmod crash

when i go to a server everythings fine but when i get shot or something or somthing blow up it lagges like hell then does the hl2.exp thing has stoped woring how do i fix that? on rp servers when i take like drugs it crashes to and like every 5 mins it crashes. I think these are my pc specs im not shure:

System Information

Time of this report: 1/2/2010, 08:56:45
Machine name: HP-PC
Operating System: Windows Vista™ Home Premium (6.0, Build 6002) Service Pack 2 (6002.vistasp2_gdr.090803-2339)
Language: English (Regional Setting: English)
System Manufacturer: HP-Pavilion
System Model: FK543AA-ABA a6667c
BIOS: BIOS Date: 09/05/08 10:24:25 Ver: 5.30
Processor: Pentium® Dual-Core CPU E5200 @ 2.50GHz (2 CPUs), ~2.5GHz
Memory: 4094MB RAM
Page File: 3863MB used, 4538MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11

What is your video card?

ATI Radeon VisionTek 256MB X1300

Try cleaning your gmod folder or putting it on lower settings.

how would you put it on lower settings?