@phreaks:what exactly are you trying to do in excel? if you're just reading data out then go with ado.net and treat it as a datasource.
for simple things i sometimes take advantage of the fact that excel (and word) can read/open html files. no interop needed for quick simple tasks of displaying grids of data with some lite formatting. just write the html file out to the browser with an excel extension header.
if you're diggin deeper with pivots and formulas, as far as i know interop is the way to go with office installed on the server. i think there are other 3rd party libs out there as well, but i have yet to have the need (would love to also hear recommondations though).