The kit is faster but that's because it's DDR2-800 not DDR2-667 and also because you will only use 2 slots instead of 4.
If your system isn't doing a lot of paging now then I would say go for the 2GB of DDR2-800. If it is doing a lot of paging you may be better with more but slightly slower RAM.
Another thing to keep in mind is you'll be approaching your addressable RAM limit with 3GB in 32bit windows.