Originally Posted by thePest

Here are the things you will need to do:
a.) change the pulleys in your rear derailleur to 8speed and the bolts. You will have a better and smoother shift. The 7's are a tad wide but will work.
b.) I would relace an 8speed hub in, be easier. But if you want to go old school. You will need to overhaul {pull out the axle) to get to the bolt holding the freehub. Go get a 8sp or 9sp {w/spacer}. The inner cone MUST MATCH THE DUST CAP on the freehub.
c.) going to an 8sp cassette {stay with Shimano} also means to replace the chain. This is a must to run an 8sp chain.

Try and stay with this manufacture when doing the change over. it will save a lot of headaches...