How do I know what size tyres can I fit on my rims? I have a hybrid bike with Alex DP17 32h rims (700c).  They still have the tyres that came with the bike on them, 40c konda's, but I'd like to replace them with some puncture resistant, narrower tyres with a slick centre strip since most of my commute is on road/tarmac path.

I can't find the rims on the Alexrims site, so how do I find out what tyres it is possible to fit?
measure the interior rim width (you need to remove your tyre to do this)
look at this chart, from Sheldon