More RAM will help. HDD space may not make so much of a difference.
Exit all other programs while using WMM to maximize the amount of RAM and processor power it has available.
Auto-save is a mixed blessing. On the one hand, it will save changes as you go, allowing you to recover from the numerous (and mostly inevitable) crashes. On the other hand, it's been known to cause crashes in and of itself, as saving requires a lot of time and effort. If you try to do something complex while auto-save is doing its thing, the whole thing will crash before the save completes.
If you want to keep auto-save, do things slowly and keep an eye out for the little statusbar icon that shows auto-save is working. You may also want to reduce the frequency of the saves.
You can also turn auto-save off, which will prevent some crashes. But if you do, make sure to save regularly, and don't try to do anything else while the project is saving.
Another thing that can help is minimizing the amount of RAM the program needs. Keep your clip library as small as possible. Keep the project size small, too, if you can. Break it up into multiple parts if you have to.
If all that fails and you're still having more crashes than you know how to handle... try another program.
