Phil,

You have a few options: 

1.  You can refill your ink cartridges.  Many forum members have successfully refilled their ink cartridges.

2.  You can buy cartridges for the Lexmark 5150 and swap the tops of the ink cartridges with those from your Dell cartridges.  I have not done this, but saw a few posts from a user that reported that he successfully did this.

3.  Modify your printer to accept the Lexmark cartridges.  A forum member posted a message about this, but I didn't see a response from this member when he was asked for details.  You will have to find out the details if you want to try this.

4.  If you don't want to get your hands dirty, you can find a place to refill your cartridges for you.  There are places you can mail your cartridges to that will send back refilled cartridges.  I found a place in a mall near me that refills ink cartridges in about an hour.

Note that I am only providing options that I have heard of and don't endorse any of the above options.

Cliff