Before you do anything, you probably wish to save any personal files you may wish to keep to a flash drive or CD.
Pretty much, if you want a standard install, you insert the Live CD and everything should work out with no problem.
If you want a custom partitioning scheme, you will have that choice. There are numerous options available. Thus far, I have found that my clean installs of Mint 5 usually take under an hour - and this is with all of the updates and a couple of downloads from the Mint software Portal.
Of course, if you hit any snags, please post so we can hopefully get you back on track. Good luck, and we should see you running with Mint 5 in under an hour, right?