To check if your card is working in in OpenGL, just goto Particles->CreateEmitter. Then hit play until you've got a few particles on screen, select Hardware Render in the Render Globals and render a frame. If you can see grey dots then you're ready to rock and roll - you can hardware render.
At this point, if you have a look at the Output Window, you should see a line that starts with Hardware Renderer.
FYI, mine says:
Hardware Renderer : vendor(ATI Technologies Inc.), renderer(RADEON 9550 x86/SSE2), version(2.0.5147 WinXP Release)
fragment API(ATI Fragment Program)
vertex API(Cg vertex programs)
Video card does not support NonPowerOfTwo textures.
And yeah, I know mine's crud.
EDIT: I'd intended to include this mel script I use for selecting the render type - much quicker than fighting your way through the dialog boxes.
window -title "Render Type";
columnLayout -adjustableColumn true;
-label "HW Render"
-command "setCurrentRenderer mayaHardware;";
-label "SW Render"
-command "setCurrentRenderer mayaSoftware;";
-label "MR Render"
-command "setCurrentRenderer mentalRay;";