Assuming you are sharing out a Printer off an XP box...
I've tried what extreme suggests and it sometimes works.
Try this:
Load the full driver on the win7-64 machine...
Ensure the printer is properly shared on the XP machine with the permissions to allow Everybody "Full Control" and all the other permissions.
Use the UNC to get to the XP machine (ie \\xpbox from run command in Win7)
Double click on the printer icon that comes up.
then in the printer control box open the Printer Properties and do a test print.
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Esle, Goto the printer's support site and get the best driver you can find... There may be a Vista 64 bit driver there...
Download it, right click, select Properties, then goto the Compatibility tab, then tell it to "Run this program..." as the version of the OS it was designed for...
Apply and OK out.
Right click on it and Run as Administrator...
With luck the code in it will be fooled enough to allow it to run and install...