Windows Vista is not only beautiful but powerful as well. The only problem are the strings attached. Power and beauty in the technology world comes with a price tag, and a big one! Most of the features integrated in Vista will never be used by you and they only eat resources such as RAM and CPU clock cycles. Turning down some unused features and visual elements can increase your Vista speed up to 5 times. This is not a clock metered number. It's just the number you will feel as soon as you make the small yet big changes in your operating system.
Turning down the visual effects. Your computer is to work, not to entertain you so why do you still use all those visual effects? By the way, all those graphics are just a way for Microsoft to sell more Vista copies, they have no professional use whatsoever. Choose Windows Basic as your Theme and reduce the color depth to 16 bits. Also replace your desktop wallpaper with a solid color instead. Just remember your computer is to work and not to entertain you.

Turn off the indexing tool. Vista has still a long way to go before making a good and fast enough indexing tool. It takes ages and it's very inaccurate the integrated desktop search tool and not only it uses a lot of hard disk space, sometimes up to 10 GB just with temporary files on a 80GB hard disk, but also makes your computer more prone to crashes because of the complexity of the system. If you want some good searches on your computer I suggest Copernic Desktop search instead, but even so... if you can, stay away from desktop search tools.

Clean your hard drive. Uninstall all the software you don't use anymore and delete all the files that are not related to your work right here and right now. Backup them if you think you might need them later. A huge number of files on the hard disk makes it super slow because of the way Windows writes the files in the hard disk. Also a huge number of files makes the disk prone to get fragmented and if you know a thing or two about fragmentation you know it's the number one reason for hard disk failure because of the extra effort to retrieve any piece of information from it.

Defragment the entire hard disk. Windows has a reasonably good defragmentation tool. Use it! If you can afford I suggest you to buy the Diskeeper 2008 because it defragments your disk on the fly.
Use the scheduled tasks to make Windows do all the dirty work for you when you are not using the computer, for example in the evening. This way you have your machine running great all the time. Clean it every week and defragment it every two weeks.
6- Increase your RAM Memory. I use 2.5 GB of it in my laptop and that's good enough.

Increase the number of virtual RAM and Pagination File size. Vista thinks he is good enough to manage this for you but I ensure you it's not. Force the Windows to use the number you give to it. I use 10GB of virtual RAM in my 80GB hard drive. It's not dangerous. Windows used to us 0GB of virtual RAM and that used to make a lot of "Not Enough Memory" messages. This way you can open almost an unlimited number of programs, software and applications with no problem.
Now restart your machine and check the differences. If your computer is not 5 times faster yet, you really need to buy a new one.