2.5 GB of RAM is not quite on the on the low side. It shouldn't be doin' that...
How large are the pictures you are adding? Make sure they are no larger than you really need. Full raster if they aren't moving, and only as large as they need to be to do any moves on them. (There's usually no need to have them larger than 2x raster, unless you are really zooming in or out.)
How full are the drives getting? When dealing with the huge files that video tends to be, best practice is to keep all drives connected to the computer at no more than 80% full, whether or not they are actually being used.
It might be time to trim your project down to just the bits you need. I find when doing longer projects that when I get to the "make it pretty part", it makes the most sense to use Media Manager to get a new project down to just the video I'm using in my timeline and the graphics and effects files that I'm adding.
I keep a copy of the whole project with everything in it, plus all the media, just in case I need to go back and hunt for a replacement shot or a new interview bite or something, but I work in my trimmed project until the project is finished.
deb