I'd just use the recovery disk tbh, however if this is too drastic then I'd suggest:
- Defragging the hard disk
- Clean out temp files & folders
- Download and install Tweaknow RegCleaner (Free Version)
- Removing any unnecessary startup items using msconfig
- Upgrade chipset drivers
- Finally, probably the best and most common hardware upgrade that techs can recommend is more memory, there's no excuse these days, seeing as you can get a 512MB stick for around £40.