Are there CD-ROM's out there on how to accurately read blood pressures?  

I'd hop on a due a search on the net, though it's likely just about everything will likely just list text that could be found in any medical text book.

Likely the best way to learn is through practice itself. Friends and family wouldn't likely object to practice, and you could likely include collegues in that as well when you're becoming more confident in your ability. You could test it and then the collegue could likely check and critique.

There are tons of information out there to let you know how to correctly read the blood pressure monitor. I would also visit my local library and get a cna book. They have tons of free medical and cd roms that you just borrow, which of course are free with your library card. Also if push comes to shove, go into a clinic or even local pharmacy and ask them to show you. If you don't want to reveal that you are a cna. Tell them you would like to know for any other reason..I don't think anyone would mind letting you know....

The local library, the internet or even a visit to your local doctor may be of use to you. But the net should contain some useful information out there somewhere.