I have been able to get my Lexmark X7675 to print wirelessly with Snow Leopard, every time.
I have both a Brother MFC-9440CN (Ethernet) and the Lexmark X7675 (WiFi), and in both cases in SL it's clear you are better served NOT installing the manufacturer's software at all, but rather use the capabilities built into SL. Of course, I installed both manufacturer's packages first, so the first few steps here were to ensure I "undid" that step:
1. From the SL DVD, optional installs, install ALL the printer drivers for all brands. You can be more selective if you like, but it's not that much space for less future headache. Find the Lexmark utilities on your Mac, and delete them. Find Lexmark pref files under user/library/preferences and /library/preferences and delete them.
2. Open System Preferences: Print and Fax. Delete the Lexmark printer there if there is one. Then right click in printing list and select "Reset Printing System"
3. Go to your Lexmark printer, and use its menu system to determine its IP address. On the X7675, it was printed out in a settings page.
4. With this information in hand, return to System Preferences: Print and Fax. Add a printer. Protocol = LPD. Address = the IP for your wireless Lexmark. Name = what you want to call it. Under Print Using, "Select Printer Software" and find your printer name from the list. Add the printer.
5. Believe it or not, open your browser. Enter this URL:
http://localhost:631 Select "Printers" from the top menu bar. In the new page, click on the name of the printer you've just added. In the second drop-down list which now says "Administration" select "Modify Printers" and enter an Admin username/password when prompted.
6. Select "LPD/LPR Host or Printer" and then enter lexnet3://ip.address:1/ where ip.address is the IP you've already identified for your printer. If it's 10.0.1.14, this should read lexnet3://10.0.1.14:1/
7. Save. Go to /Library/Printers/Lexmark/PDEs folder and delete the entire PDEs folder.
8. Open up Software Update. It may find a "new" Lexmark driver package. Install it.
9. You should be good to go. Print a test page from your computer. Tip: in SL, when you've sent a job to the printer and its icon opens in the dock, I like to right click/options/"keep in dock" for future easy access.