No, amps that are 2-ohm stable mean they can handle any load DOWN to 2-ohms. However, many 2-channel amps are only stable bridged to 4-ohms. So make sure what you have or want matches up.
You can run a 2-ohm stable amp at 4 ohms just fine, but not 1-ohm. (make sence now?) However, there is a penaly... Power is a result of the calculation of current and resistance. They are (for the sake of argument) static so you can only change them with the speaker. Your amp is X power and your current is what ever the amp needs so you can only change the resistance. However changing this changes the power too.. Sucks hu... Nah... really, it's simple...
Think of it this way... The common resistance rating for all MOBILE audio (home is different) is 4-ohms. Everything is rated off this scale. Most fill speakers are 4-ohms and most subs are, or come in, a 4-ohm version. Subs are also common in 2, 6, 8, and 12 ohm variations which are all deisned for specific reasons.. But 4-ohms is the 'standard'.
(this following statement isn't always true but often it is and it gives you an idea of 'why'):
Now say your amp is 150Wx1 @ 4 ohms but it's also 2-ohm stable. You could add a 150W, 4-ohm sub off of it OR you could wire two 150W 2 or 8 ohm subs off of it and they'd have the exact (or very close) power. If you wanted to run a DVC sub that was 150W/coil stable, use a 4-ohm DVC sub and wire it for 2-ohms. The 150Wx1@4ohms amp is a 300Wx1@2ohms (often...) RMS amp. You get more power out of the same amp due to the changing resistance. As long as the amp can handle the increase in duty, no problem.
Now if you get an amp that is 300Wx1@2ohms for that reason and then stick a 4-ohm load up to it, it's now only a 150Wx1...
That's about the simplest way I can explain it.. If you have an amp or a sub and want to know what amps or subs to look for, just ask. If your buying all new, just let me know the idea of what you want and I'll help you match up exact components. (Many subs, like JL, come in multiple versions (2, 4, 6, 8, and 12 ohm and 2, 4, 6 ohm DVC) so you can wire them up exactly how you want them.)
For those who are still a little lost on that fact: You can take two 4 ohm devices and show 2 ohms or 8 ohms (but not 4 ohms) at the wires just with changing the way that you wire them up. See section 38 for the basics on series/parallel wiring here