2
Xoops 2.0.14 works with Php5 - although some scripts will produce messages (not errors) if you have debugging enabled.
We've a number of FAQ's regarding blank pages - which can have a number of causes depending on server or XOOPS set up... best thing to do is to have a good look through them, and see what helps you there.
It's hard do say which version of XOOPS "popscript" is based on... without examing the code further. I've heard some people say that it's based on XOOPS 1 (which is very old) ... but I would suggest if you wish to try to upgrade to a newer version, please backup your site and database first.
In fact, it may be advised to attempt an upgrade on a local machine first...
Xoops 2.0.14 will upgrade from any version from 2.0.10 upwards (although XOOPS 2.2.x requires more work...) - so, so long as your site is based on this - upgrading may be quite easy.