Windows 7: Switch to 64bit. My system has two hard drives.

You've missed the point - rldupree was concerned about losing data, my post indicating that partitions - ALL partitions get wiped, and my suggestion being he should remove / disconnect the 32bit disk before installing.

I could probably say the same thing. If there's data to be saved on the secondary drive, and there's no plan to dual-boot (thankfully) then dump all important data to the data drive, aka the secondary, and then freely wipe out the entire primary disk...once it is disconnected. Then the OP only has to reconnect the drive after x64 is installed, and all the data is available.

Just to point out: a clean install will NOT wipe the entire drive. In fact you can save ALL you data from the old install even after installing over it.

The clean install will only install over the partition you point it to (which may or may not be the whole drive).

If you install over an existing install, all your data will be moved into the Windows.old folder, from which you can save it.

~Lordbob

Good point Lordbob.

If the OP wants to keep the recovery partition and doesn't need the space, the Windows 7 64bit can be installed on the current Windows 7 32bit partition.

If the OP wants to use the recovery partition space, He/she should consider if there will ever be a need for the origional OS. For example sometime in the future if they want to sell the computer and keep the Windows 7 upgrade.
Most OEMs have a utility to burn the recovery partition to a DVD, saving it if needed later.
Then the recovery partition can be deleted.

Good point made previously, should confirm it is two physical HDDs and not two partitions.

All this can be easily done if the OP returns with a little information.

Lordbob said it already, but I will dare repeating - the installer does NOT necessarily wipe out all data in the machine, as you seem to be suggesting. It's possible it has an option to do so, but it's only one option.

The machine I am using now - I am dual-booting. Windows 7 was installed on a separate physical drive, but you bet I did not disconnect the other physical drive before installing and nothing happened to it. The recovery partition is still there as well. In fact, the installer is rather flexible, you just have to pay attention to the questions it poses to you.