Assuming that you don't want to spend any money, then back up data and do a complete wipe and re-install of OS, eliminating any non-essential add-ons. That should speed it up more, and for longer.
If money is no object, the only thing that would speed up the system (RAM is already maxed at 2GB) is an SSD drive - but it would have a significant effect, even cloning the existing installation onto it.
If money REALLY is no object, then replace Vista with Win 7.
If money REALLY, REALLY is no object then buy a new laptop!
SD