Defragment the hard drive. Defragmenting at least once a week will help maintain quicker access times. Schedule to do this overnight.
Utilize two hard drives, using one for audio files and projects exclusively. With hard drives now running in the terabytes, it makes storage space problems virtually disappear. If multiple hard drives isn't possible, settle on partitioning the hard drive.
Disable write-behind caching on the hard drives to improve disk access speeds. In Windows XP, this is done through Start>Settings>Control Panel>System>File System>Troubleshooting. In Windows 7, Start>Control Panel>Hardware and Sound>Device Manager. Right-click on the hard drive, then click "Properties" and "Policies."
Disable any screen savers and background images, as they can take up considerable processor overhead. In Windows XP, right-click on the desktop, click "Properties" on the Screen Saver tab. Click on the Menu arrow and choose "None" for the screen saver. Click "Apply." Then click the Desktop tab and on the pull-down menu choose "None." Click "OK."
In Windows 7, click "Start," "Control Panel" and "Appearance and Personalization." There will be a small list of links underneath. Click "Change the Theme." At the bottom of the page, click "Desktop Background." On the pull-down menu, choose "Solid Colors." Choose a light color---the lighter the better---then click "Save Changes." Click "Screen Saver," then the Menu arrow, choose "None," then press "OK."
Restrict usage of all kinds of audio software. Only install what you're genuinely going to use. There's nothing wrong with installing demos to see if it's something you'll use. However, once you realize whether it's something that you'll utilize, uninstall any extraneous software. This speeds up DAW start-up as well as switching between DAW arrangements.
Update the drivers to your software and hardware regularly. Check about every four months or sign up for their email newsletters so you're informed when the updates are released. In almost every case, new drivers will improve performance and may add extra features.
Don't use Windows Vista. Overall as an operating system it has more problems and stability issues than Windows XP or Windows 7. Wait to upgrade or downgrade.