Size of Windows Vista Build 5728

i'm currently acquiring windows vista x86 build 5728. i decided on going with the 32-bit version as i've never even tried windows xp x64. how much room does winvista take up after install and all patches (if any or whatever) are done? i have my winxp pro 25gb and am using 10gb of it. i like giving my os' some elbow room. i'm using this as a dual boot os as i just want to test out the latest beta of this os for i've heard good things and much bugs have been squashed. it's also free! also, how do the keys work for said prog? pm! thx.