what is your current config dude?
I know there was an upgrade to the 5690 some point in the past but it involved a mobo replacement.
As long as you stick to 478 pin CPU's you can upgrade them within reason.
Memory can be expanded to 2GB
DVD/CD can be upgraded to DL DVD burner (NEC ND-6500A recommended).
Internal disks can be upgraded for speed, capacity or both.
The GPU is fixed (except for the mobo upgrade) as is its memory.
About the only other thing is changing the LCD resolution but that is a big job.