Are you trying to install the Lexmark X4550 to your Mac computer? What is the exact OS of your Mac (i.e 10.3.x; 10.4.x or 10.5.x)?
You have to make sure that the pinter is compatible with the OS that you have.
I don't have a doubt with the printer since you mentioned that it worked with XP. To install the printer to your Mac, please follow the steps below:
If your printer does not appear in the Printer pop-up menu, find and
install the appropriate driver. Check any CD-ROM discs included with
the printer, or the website of your printer's manufacturer. Only users
with an administrator account can install software.
: You can also open the Printer List window from Printer
Center (Mac OS X 10.2.8 or earlier) or the Printer Setup Utility (Mac
OS X 10.3 Panther, or later).
Check the Printer menu again after installing the software. If the printer does not appear, you may need to do this:
- Make sure the printer is connected to your computer, plugged in, and turned on.
- For Mac OS X 10.2.8 or earlier, from the Printer menu in the print dialog choose Edit Printer List. The Printer List window appears.
- For Mac OS X 10.3 or later, choose Show Printer List from the View menu. The Printer List window appears.
- Click the Add Printer button.
- Choose USB from the first pop-up menu.
- Select your printer from the list.
- Click Add.
- Close the Printer List window.
If the printer will not work, you may download the driver from the Web and install it. Here, I have provided you the link where you can download the printer driver:
Just click the download button and install it.
Have a great day!