You could try bumping the RAM up to 2GB, but I'm not sure how much that would actually increase the performance.
One thing you could try to actually increase the peformance of the video during editing though, is buying an additional hard drive, and having your video files on that, whilst keeping your OS and applications on the main drive.
If it was a choice between the two, personally I'd go for the extra hard drive, if mainly for the reason that when you're doing lots of editing, even though 250GB sounds like a lot, there's no such thing as too much hard drive space
