I'm guessing that the one Windows 7 machine is 32-bit, and the other (with the driver problem) is 64-bit.
I'm also assuming that you're connecting to this printer via a share from the SBS server.
So if my guess and assumption is correct, you'll need to get the 64-bit driver into the SBS server so that it can send it to the Win7 64-bit system when it tries to connect to that printer share.
The first trick to this is that both the 32 and 64-bit drivers need to be the same name, or they won't both associate to the printer.
Go get the newest driver(s) for that 2600n printer from HP: 32-bit here, 64-bit here
Replace the existing 32-bit driver (at the server) with the one you just downloaded.
Then install the 64-bit driver you also just downloaded -- The trick here is that if SBS2003 is 32-bit, you can't load a 64-bit driver directly, you have to do it from the 64-bit client:
On the x64 machine, from Start > Run, type \\servername, where
servername = the name of the x86 print
In the list of shares, open the Printers folder.
Right-click in the Printers folder [window you just opened] and select
Go to the Drivers tab [select the x64 driver] and add a new x64 driver.
The above steps were obtained from here, which explains it pretty well.
If my assumptions and guesses are wrong, you'll need to provide more applicable information before we can help you. :)