In short if you have a Joomla 1.5 website that relies on Virtuemart, I wouldn't go beyond 1.5.3 yet. Virtuemart are still only at RC2 for Joomla 1.6 and none of the modules work yet. I thought I'd have a try at upgrading though to see what happens.
First thing I did was take a full site backup so I could rest at ease as I butchered the site. I went ahead and downloaded the Jupgrade component and when I tried to run the upgrade, it kept hanging on the checking requirements screen. The Jupgrade instructions recommend to uninstall anything that is J15 only which includes Virtuemart. Then I continued disabling plugins until it eventually ran.
You then realise that your site is still the same because all that Jupgrade has done is create a second site in a sub folder called /jupgrade. So you need to go in via an FTP client and blow away the old site and move all the jupgrade contents to the root folder.
First thing I noticed is that it was version 1.6.3 of Joomla which then needs to be updated to 1.6.5 to be stable. And virtuamart was gone because I had to uninstall it to be able to upgrade Joomla. I then installed virtuamart 1.9.8. On the virtuamart site they say the core is compatible with Joomla 1.6 however when I installed it I just got a PHP error. It was at this point I confirmed for myself that if virtuemart is required then its best to stay with Joomla 1.5.3 for now.
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