Jon Austin , Nov 10, 2004; 12:36 p.m.
If your lab asks for sRGB, then it means that their equipment is optimized for that color space. Also, if you shoot your images in sRGB, and then convert them to a "larger" color space, i.e., Adobe RGB, you will have gained nothing. You'll just have the same (sRGB) color information in a larger (Adobe RGB) "container."
To benefit from the wider color space, shoot in Adobe RGB, and then take your images to a lab that provides Adobe RGB output. Otherwise, I dare say you're wasting your time.
As an experiment, capture an image in Adobe RGB, process it as usual, save it, then convert it to sRGB and save it a second time as a separate file. Send the sRGB version to your current lab, and the Adobe RGB version to a lab that uses that color space, then compare the results.