Several questions before upgrading from Windows Vista Home Premium to Windows 7

I’m currently running Windows Vista Home Premium (upgrade from XP) 32 bit and planning to upgrade to Windows 7 64 bit. I have 2 drives C&D, OS is on C. I understand that I will need to do a clean install to go from 32 bit to 64 bit. My question is:
Since I have a lot of programs on the “Dâ€Â￾ drive will I have to reformat that drive also for 64 bit or will I be alright the way they are. My largest program is World of Warcraft which is huge. I’m not so worried about reloading other programs which are much smaller.
I'm not a noob but also not an expert. So please keep responses in somwhat laymans terms. Thank you in advance for the help.

Thank you for the information. I'm looking forward to going 64 bit.

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