I used the look-up table for the exact same application, a thermistor. Here's what I did:

Use an Excel Spreadsheet to calculate what the tempurature is for each possible A/D count. If you're using 8-bits then that's great because you get 255 entries in the lookup table.

Use the lookup table with the A/D count as the index. In the actual table insert in order the tempurature entries you calculated in the spreadsheet.

So your code will look something like this:

Lookup adcount, [120, 119, 117, 117, ...]


If that's still not clear I can send you my spreadsheet and code when I did it.

And if you could help me out with my HSerout problem I'd appreciate it. See my other post.