I found a way to fix the problem if you are using Vista, like I was. Apparently, because I am using an older printer, there indeed was a compatibility issue with Vista and it had nothing to do with doPDF. Here's the solution that worked for me:
Installing a Network Printer in Vista:
1) Hard wire the printer to the Vista "client" PC or laptop, as though it were to be used with that computer, and install it. This ensures that it has all the necessary software/drivers on board. (This step is important for this fix to work)
2) Reconnect it to the "host" PC and, in its Properties, set it as "shared". Make a note of both the host PC's "Computer Name" and the printer's "Share Name".
3) In the Vista "client" PC, launch the "Add a Printer" wizard and select the "Add a local printer" option. This automatically opens a new dialog box in which to select the Port.
4) Click the "Create a new port" radio button and leave the drop-down menu options on the default of "Local Port". Click Next.
5) A small box opens in which to enter the Port Name. Type in the path to the "shared" printer in the host PC using the format \\computername\sharename where computername and sharename are the details you noted in (2) above.
6) Select the Printer driver from the list provided, which should include the driver you originally installed, otherwise use the "Have Disk" button to install the correct Vista driver if it is not in the list. It is essential that a Vista-compatible driver for your printer is used. Click Next. If you get a dialog box that tells you "Windows detected that a driver is already installed for this printer", click "Replace the current driver"
7) Give the printer a name and choose whether to set it as the default. Click Next.
8) Print a test page to verify functionality and then click Finish.