There are multiple ways to go about this:
1. If you have the OEM edition, contact your computer vendor for a 32-bit install DVD. If you have the retail edition, contact Microsoft. If you have the :sneaky: edition, find a 32-bit install DVD somewhere.
2. Use virtualization software such as VMware Player to install the 32-bit edition of Windows.
3. Try to get your software to work with 64-bit Windows.