I bet a lot of my friends know me and that I'm a complete freak when it comes to keeping my Laptop in shape. I've messed up loads and loads of times and it's very very likely of me to pop in a Vista install CD every once in a while and do a fresh install. But it's been long since I've done that. I think I've messed up my Laptop so many times with dualbooting and bad software that I think I've now reached a point where I can avoid messing up.
Alright so here's what I do to keep my Laptop in shape...And yeah this is for Windows...All you Mac fanboys shut it!
 
Run Ccleaner atleast twice a day. 
Run Registry Mechanic atleast once a week. 
Run Smart Defrag everyday - Defrag and Optimize all my disks 
Keep my desktop free from clutter - I use Stardock's ObjectDock which gives me a Mac-like dock to put all my stuff in. 
Uninstall any programs that I don't use. 
Run the Windows Disk Cleanup Utility. Just search for Disk Cleanup in your Start Menu. 
Keep only one application to do a task. Don't install 3-4 media players to play your mp3s. Same goes for browsers. 
Regularly install important updates from Windows Update. 
XP users need to install an anti spyware software - Vista's already got Windows Defender. 
And lastly, a good antivirus software - I recommend Kaspersky Antivirus. I was using NOD32 but fell prey to a virus that it couldn't detect or remove. I installed Kaspersky and voila! problem solved.I think if you follow these instructions - any Windows PC would work wonders! My laptop stays on for months at a stretch without having to restart due to crashes etc. I don't know why people crib so much about Vista..I absolutely love it!