I guess my original question is: should I expect to have the same clarifty on my IBM flat panel as I do on my IBM TP screen?
Yes, however there are caveats:
1. You need to run the T40 at the same resolution as the native resolution of the external LCD, which in the case of the L180p is 1280x1024.
2. As G-man says, you'll get better clarity with the DVI (digital) interface than with analog. The T40 has only an analog VGA connector at the back. In order to get DVI, you need either a Port Replicator II or a Mini Dock, both of which have an external DVI connector.
3. Assuming you're running WinXP, you may also want to experiment with ClearType. Some people (e.g. me) find it makes a big improvement, however others find it objectionable.