CD/DVD oddness... I put in a dvd or cd and vista thinks it is a blank dvd/cd and asks me to label it. Oddly enough if I right click on the drive and select eject then reinsert the disk vista recognizes the content. This happens to me on 3 different vista machines (all dells).
Oh wow there are so many things to check.
1) Same model of Dell? (Could be the specific model of reader/burner.)
2) Are the three machines in close proximity? (I've had an entire row of machines lose their DVD readers... the top row... because of the heat, over time.
3) What does it say in the event log on those machines? Anything regarding the CD?
4) Does it do it to Audio CDs too?
5) If you upgraded to Vista, it could be this.
My bet is on CD burning Software. this link can help you to digg in, as Mark Allen pointed out.
I have seen similar issues and it can be sometimes attributed to corrupt or missing upper and lower filters (installed by Burning Software, etc).
(Please note the below is very similar to Mark Allens link...unfortunately NoScript was causing me not to see his link...while it is a different KB I linked, it is for the same issue (which can effect even non-upgraded PC's)
A quick warning, modifying your registry can cause undesired results...so take what I put below with caution.
Additionally, you can take a look at the MS KB. Q314060.