MSP won't create preview files

[Tamale]

hello
i've been using MSP 6.0 for about three years now. really like it a lot and does what I need to do with no problems, until recently. i start a new project like i always do, start editing and pulling clips into the timeline. now when I hit the play button in the Preview window, it plays the entire timeline for me, but i noticed it's not creating any preview files. so when i begin moving clips around and adding transitions, the application would crash.

my system is a Dell 8400
120 G HD
1 G RAM
2.99 Ghz
Nice video card
Windows XP

can you tell me why it's not creating preview files? is there a setting i should set? i opened an older project and if i make a change to the project, i hit play in Preview Window, and I see that files are being created (bottom status line). any help would be great.