in fact, it should be fine as long as you install wamp in each os in its partition and as c2dan mentioned, you have to be admin w/ full privilege when installing wamp; to make it more clear, here is example: when log into xp, you will see xp parition is C: while vista is D: and vice versus when log into vista, you will see vista partition is C: while xp is D:, but no matter which os you log into, you still install wamp on C:
Have fun,
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