I have installed CMSMS as a test on my PC running WAMP5 and it worked a dream

Have now stepped up and am installing it on a server running IIS5, and have got it to the install part

At the first page (1) it passes all requirements, but has the yellow warning next to 'Checking if sessions are enabled' (and PHP memory is 8mb, upload mem = 2mb - but not so wurried bout these).
I have checked the php.ini file and the sessions section is the same on the server, as it is on my PC.
I'm not really sure what else to look for (and bit of a newbie to PHP). Been looking on google extensively but can't find a solution.
Can anybody point me in the right direction?
Or do I even need to have sessions enabled? - the site needs to run the built in modules plus calendar module.