Stock is 5.25's (round) in the doors and on the back roof. You can buy 4 matching speakers and put them all in with the stock mounting holes. The doors will also support 6.5's (round), but you have to drill new mounting holes, which is really no big deal.
On the whole it's pretty darn easy, especially if you get one of those installation pamphlets from crutchfield. It will walk you through.
2007 WK Overland
5.7L Hemi QDII - 200k+ Hemi Club #88 | Black WK Club #151