Windows 32/64 bits load .dll

Hi to all:

I have an application that are made in 32bits throught vb.net 2008...This apllication work with an .dll that only run in 32bits...
Because of this i had install the app in a PC that have Windows7 with 64bits, in the folder Program Files(X86)...The app start and run well, but when enter in the form that need to run the .dll that i had mentioned the App give and error and leave exit...
I had install in a PC that have Windows XP 32 bits and everything work well...

I don't know if i had do something wrong or if i must something more, and a help it was fantastic


Thanks