Help with CSS lag despite of high FPS

[sweetnsexy]

im playing counter strike source on a HP - Compaq Pavilion Slimline s3210.me Desktop/PC..
specs are :
1.6ghz x 2.
1gb ram
ati radeon hd 2350
250 gb sata hard drive
and i play css on low setting and i get like 90 fps and ping is around 40.
i lag every minute for like a few seconds and choke becomes like 45-50..
rate 25000
cl_updaterate 100
cl_cmdrate 100...
help pleaseee

 

[mopar man]

Do you have ANYthing running in the background?

Is this on all servers?

Did you install something when this started occuring?