If it's a 15-pin d-sub connector, that's "VGA." Modern computers generally come with a DVI (more common at this point) or VGA connector (still common enough). DVI is a standard that can accommodate both a digital video signal and an analog one. VGA is just the analog signal, although it can get plenty high res and deliver very good picture quality.
In almost all cases, DVI ports carry both signals (this is called DVI-I, where I is for integrated; a DVI port that only carries Digital or Analog would be DVI-D or DVI-A). That means that on most computers with DVI ports (all current Macs), you can use a DVI to VGA adapter.
The only thing to be cautious about here is that with the Macs that have mini-DVI ports (actually, not sure if anything does right now?), the mini-DVI to DVI adapter only carries DVI-D. So you have to buy the Mini-DVI to VGA adapter; you cannot stack the Mini-DVI to DVI with a DVI to VGA.
Out of curiosity, do you have a specific reason for wanting a CRT? They're huge, they're heavy, and they waste a lot of electricity. The picture quality is better in some cases, but even almost every single graphic designer I know uses LCD at this point....