Hi

Of course a PIC can connect to a serial thermal printer. Most printers come with either USB , parallell or rs-232 and very few have more than one interface. When using a PIC the rs-232 is the obvious choice. You only need a MAX232 or a MAX3232 (if you have a 3.3v pic) and then it is enough to connect the TX and RX (if you want to poll the printer status) and Ground. Most printers can work in either text mode (using internal font set) or graphic mode (where you need to format every little pixel yourself an send this data to the printer. Text mode is easier and usually prints faster, plus using less codespace in the PIC.

We are using Epson TM-88 III or IV versions or a TM-90. The TM-88 IV is fast as hell to print. Most Epson printers have an internal memory area where it is possible to upload picture logos using a PC (TMF logo software). This will allow you to get graphic mixed with text and still not need to handle the actual logo in the PIC. You just tell the printer to "print logo nn". The result is a mix of text and graphics, most POS machines uses this way since it is fast to print.

Most printers have a removable communication board in the back so it is easy to change so if you have a printer with USB just get a serial board and plug it in.

Ebay is a good place to start looking, just make sure you get a rs-232.

Different brand and models of printers uses deferent command codes. Even Epson TM-88 and TM-90 does use exactly the same command set but most parts are similar. You can find Epson command set on internet and if you really really look you can find their programmer's reference guide which is gold.