I just fired up ID CS3, opened a file and selected Mangal as the body copy. It displayed just fine, and the Hindi characters showed up in the Glyph palette...

I think that to do Indic scripts correctly in InDesign you have to use an add-on like ScribeDoor

http://www.winsoft-international.com/en/products/scribedoor-for-creative...

Otherwise the required vowel reorderings and complex consonant ligatures (conjuncts) will not be produced.

For InDesign CS3, I think the only way to do Indic scripts is with the IndicPlus plug-in (Windows only):
http://metadesignsolutions.com/indicPlus

For CS4 or CS5 there are several other options, including ScribeDoor and World Tools.

Nick — To truly display Indic scripts properly, the text engine needs to be able to process several Indic-specific OpenType features for vowel positioning and compound consonant conjuncts (as Tom mentions). So, even though the typefaces show up and the characters are all there in the glyph palette, that’s not quite the same as being able to use them, practically speaking.