Marjolijn,
Kirk is correct that there is no direct way to import Excel data, but it can be done with a little effort. Given you have 2000 images, I think it will be well worth your time.
You'll need to become familiar with Code Replacements. See the section in the PM pdf manual that discusses this.
Next, you'll have to output your Excel file to a text file in Code Replacement format. Suppose your Excel file looks something like this:
img_500 mycaption500 mykeywords500
img_501 mycaption501 mykeywords501
What I do is create another sheet in the workbook that looks like:
img_500a *tab* mycaption500
img_500b *tab* mykewords500
img_501a *tab* mycaption501
img_501b *tab* mykewords501
where *tab* is the tab character. Note I need to add an 'a' and a 'b' to the filenames to distinguish which field they will go in.
Once the CR file is in place and ready to use by PM, the in then IPTC Stationary Pad:
Caption field ==> /{filenamebase}a/
Keywords field ==> /{filenamebase}b/
Apply this Stationery to the 2000 images and you're good to go!
I've probably skipped a detail or two, but hopefully this gets you started.
This process would be made *much* easier if some of the suggestions in this thread found their way into PM:
http://forums.camerabits.com/index.php?topic=2958.0Deven