Google is your friend here - I googled "Brother PT-1230PC Linux" and the second link to come up was this:
Executive summary: Brother does not provide a Linux driver but this program works well for me in 11.10. Brother's Linux drivers for labellers are here - they usually provide excellent Linux support but the PT-1230PC is absent from this list. Doesn't matter, B-Label works just fine!
Install the dependencies using:
apt-get will tell you if you already have these and install the missing ones.
sudo apt-get install libgtk2-perl libgtk2-gladexml-perl libgd-gd2-perl
Insert the tape and batteries into the printer, plug in the USB cable and turn it on. Ubuntu will recognize the printer but can't find drivers for it. Don't panic, just open CUPS by typing:
into your web browser, click "Adding Printers and Classes", "Add Printer" - you may then have to supply your user name and password. The PT-1230PC should appear under "Local printers", select it and continue. The next page with the printer name and model should be filled in for you, modify it if you like and continue. On the next page, instead of "Brother", choose "Other Manufacturer", "Generic text-only printer" as the B-Label page instructs. CUPS should then tell you the printer has been successfully added.
Then extract the blabel.zip file into a folder (I used "Home" - "Programs") and double-click the "blabel" file.
One note of caution - do not use 72 point Sans. It only printed the last two characters and stopped. 72 point is too large anyway, the characters are cut off top and bottom. I verified this twice. 40 point Sans worked fine though. I'm not sure how large you can get it, the labeller only comes with a sample tape and replacement tapes are quite expensive so I didn't experiment around. I e-mailed the developer about this.