Create a new partition on your PC and install it in that.
If you don't know how to that, I would suggest thats a hint you might not know enough to want to try playing with the 64-bit version since, as mentioned previously, most of the drivers for your machine might not exist.
And not just the easy ones like printer drivers or sound cards, I'm talking system ones like memory bus drivers, etc. etc.
I had a go.
Most of the aforesaid drivers were missing.
I gave up, and deleted the partition and went back to 32bit XP on the original partition...
RH