Tables in Word XP are slooooow! I don't remember this problem in Word 97even before I upgraded from my ancient 486. What's the problem?
Well, it's pretty much as you say: tables in Word XP (not to mention Word 2000 and 2003) are slower to load and redraw than tables in Word 97 and previous versions of Word. This is because the later versions of Word have to be able to create HTML tables, so they use a different (and slower) table engine. Nested tables slow things down even more, simply because they're more complex.
To minimize this annoyance, try the following:
Turn off automatic cell resizing if you've left it on for any table. Right-click the table, choose Table Properties, click the Options button, and uncheck the "Automatically resize to fit contents" box.
Keep tables short, if possible. If you have the choice of creating 10 short tables or a monster table with 10 subheadings, go for the 10 short tables. Eliminate merged cells if possible; they're useful for subheadings, but they slow down Word's handling of tables.
When editing tables for content rather than layout, work in Normal view rather than in Print Layout view or Print Preview. Also try turning off background repagination: choose Tools » Options, click the General tab, and uncheck the "Background repagination" box.
Keep rows shallow if possible. Instead of putting a dozen paragraphs in a row, create a dozen rows. Use borders to differentiate them.
Keep your tables as simple as possible. Don't wrap text around tables unless you mustand if you must, do so when you've finished creating and editing the tables. Use as few graphics as possible in your tables, and when you do, put the graphics inline rather than having them float.