32 or 64 bit choice on upgrade?

Alright, so I pre-ordered the Professional Upgrade (he he, got it from Newegg.com and got it for $99 a few months back! ) Anyways, I have a pretty awesome custom built PC and I'm thinking that I should install 64 bit to use all 8 GB of RAM. I'm wondering if during the upgrade, it will like let me choose between 32 or 64 bit? Also what are the pros and cons of 64 bit? I currently have 7 RC 32 bit installed. (I only have 4 GB of RAM in it now, I just ordered the other 4 GB so I could put it in later) Also, will 64 bit hinder the ability of some of the programs I want to use? I've heard that Realplayer won't work in 64 bit. (Is this true for RealplayerSP?) Will it make games not work? Will there be driver conflicts with this set up? Thanks for your input!

My PC.
Coolermaster Elite 330 with two Thermaltake 120 MM fans and a Rosewill silent 530W PSU
AMD Phenom II X4 810 2.60 GHz Quad Core
ECS GeForce 8200A ATX Mobo
8 GB (4 x 2GB) OCZ Blade DDR2 PC6400
Western Digital Caviar Black 500 GB Sata II
Sapphire Radeon HD 5850
Wireless N
LG DVD Burner with lightscribe.

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