Definitely not if you're doing something like idly or dosa, but if you're a beginning indian cook, you're not likely to be doing something like that.

Different lentils do have different flavors, and Indians can be real snobs about what kind of lentils they use, but as long as you're not cooking for any actual indians, I'd say go for it. BUT, as you start doing more indian cooking, start finding the right kinds of lentils for different dishes, it'll pay off.

I would think for a soupy lentil dish (dal) where the lentils are the star, and not ground or mashed, that substituting would be OK. It may not be absolutely authentic flavor, but I have sub'd grocery store lentils, and even split peas, for the red/green/yellow called for in some of my Indian recipes. The taste might not be 100% authentic, but I think it would still be acceptable. However, as a processed ingredient (as in idli, which are sublime when made correctly), I'd be reticent to substitute. In that case, I'd just gaze longingly at the recipe and wish.....

we use this dal(Lentil)for making idli

thanks!

This link might help you decide:
http://www.recipetips.com/kitchen-tips/t--975/all-about-lentils.asp

I haven't tried that substitution myself, but if you're not too picky about the end result, I'm sure it'd be fine in most dishes. If you're making Idli, I wouldn't make the substitution because they rely on a specific fermentation process that won't turn out properly without specific ingredients. (I can tell you that one from experience!)

http://en.wikipedia.org/wiki/Idli