I'm currently using a WD100 (10GB with 2.61GB free) in my computer. I'm thinking about switching to a WD800 (80GB with only XP sp2 installed). Is there any real benefits to doing this since I also have a Maxtor 80GB (slave) installed? Will there be any noticable changes in performance?

Newer drives will have faster read/write access time, so in this case Yes

Personally I would switch to the 80gb drive as your main drive with operating system on it and use the 10gb hard drive as a slave drive for storage/programs etc..

Depends on what your reasoning is, is your computer running slowly? Taking a long time to load programs? What is your computers compleat stats? Ram? Processor? How old is it?

There could be any number of reasons your computer is running slowly,, however a quick fix is to reinstall windows, this will erase any settings you have but you will keep all personal files and such... I do recommend you back these up first.

What is the stats on the HD's? Depending on that I would do as seawk recommended also, but this is depending on the stats, most likely your 80gb is newer and therefore is problay better equipped for running as a main drive. Post the stats back and well see what we can do.