I wrote a little Perl script to convert a comma separated value (.csv) spreadsheet to TeXmacs table format. Ugly, but it worked for the table I needed for a school lab report <smile>. Please find a copy attached.
I ended up using Emacs to insert it into the TeXmacs file. I tried using "Insert - Link - Include", but that showed up a bunch of tags instead of as a rendered table. I suspect it is because my script doesn't write out <body> tags etc.
If there is a better way of importing spreadsheets please let me know, but if I remember the documentation correctly the other workaround is to convert the table to EPS and insert as a figure.
Thanks to all who support TeXmacs!