MSI 9800GT Temp is 48 ?

Sounds like the cooler is working quite well to me. Anything under 55C while under full load is quite good! Idle temp could be lower, but that all depends on the temp inside the case.

With what program are you monitoring the temps?

I have the same MSI 9800 GT as you. I run them SLI and after 10 minutes of Crysis on high settings, they'll go to 75 C. However if I set the GPU fans manually to 100% and leave out the case side panel, the temps max out to around 68, 69 C.

Under load, your card stays cool compared to most 9800 GTs. 48 C at idle is very normal.

80-90ºC is average
115ºC is threshhold
127ºC burnout

Remove the dust from the fan. Reapply thermal paste.