Web site moved and now won't cache

I moved my web-site to a different hosting company and now none of the pages seem to cache in IE 5, 5.5 or 6.
I've got a 40k background image which is the same on each page and it downloads it each time on the new site - on the old site it didn't. None of the pages appear in the temporary internet folder.
If I go to the old host that has exactly the same files, then they subsequently appear in the temp files folder.

Any pointers?

Pointers..

I guess your new server is sending "expired" headers. I'm no expert on that, but you can compare your two sites here:
http://www.ircache.net/cgi-bin/cacheability.py

And read about caching here: http://www.mnot.net/cache_docs/

After doing so, take a walk and ask your self WHY you ever wanted to move your site :)

I tried that - the 2 sites show up identical - green and validated, other than the new site that doesn't cache is running Apache/1.3.35 and the other caching one is running 1.3.26.
I am asking myself why I changed - especially as the other one was free with my ISP!