I get the same thing sometimes with Premiere Pro 1.5 on a system with 2G of system RAM.
Adding RAM is always a good idea and you are probably “underpowered” with your system. If you can double the amount of system RAM you have, you will notice that everything is less sluggish and you will need your hard drive less for virtual memory or “scratch disk memory” in general.
I usually go to Crucial’s website to determine how much RAM I have and how much I can add. Crucial has a nice little widget that you can download that will determine everything for you. This is not to suggest that you must buy from them — but they will give you the exact specifications for the computer you have.
I would not purchase RAM from any company that does not offer a 100% no-questions-asked lifetime warranty on RAM.
I note the same issues with version 1.5 and many of these are attributed to the application “conforming” material that I have added to a bin. Additionally, I notice that the application will get sluggish when I have lots of layers in an edit.
Adobe applications sometimes do not release memory when they’re working and the best way to clear out things is to exit the application and then start it up again. If you are running several applications (Photoshop, Illustrator, a web browser and so on) it is sometimes helpful to log out completely and then log back in, or do a restart sometime in the middle of your day (assuming you’re editing all day). This clears out all allocated RAM that ought to have been released to the system but wasn’t because one application or another doesn’t clean up well after itself.
Vince is correct that maxing out your RAM might be expensive and the theoretical limit of a Windows 32-bit application is 4G of system RAM. I doubt that Premiere can actually use more than 3G of RAM though, so the maximum useful RAM you can put in your system is 3G.
But if you must add RAM in pairs for your computer, Crucial will tell you that and you should follow their directions, adding 4G to get 3G of useful RAM.
What if there were no hypothetical questions?