Hi, I would like to add some comments for you in addition to those provided by john-auvil, and by the way he is right on the money.  MEP provides some really amazing features like transitions, special effects, title, etc.  All of which consume memory when trying to mixdown, render, and burn a DVD, or even export the production as a file.  The MPEG 2 format of encoding while it is the broadcast standard, and most DVDs that you buy use this format, it too consumes large amounts of memory, much larger than the MPEG 4 format.  If you select HD1 or HD2 when you try to burn or export instead of say DVD, you are looking at consuming even more memory.  Add to that any applications that are running in the background such as web browsers, email apps, windows widgets etc, and your 3GB of RAM can very quickly be allocated out to other applications and not the burning process. Disc accest times for both your hard drive and your DVD drive will also impact speed.  I run a Quad Core CPU with 6GB of RAM and that often does not seem to be fast enough.  Windows XP is also notoriously slower than Window 7 in handling video. 

When you go to burn shut down every application that is not related to the Windows OS and your burning application.  Also load one of the videos that used to burn quickly into MEP and see how long they take to burn.  Please let us know what happens.