I will probably try PostGreSQL for my needs as it seem powerful enough and easy to ship to my potential customers. For the data provider i will try npgsql as you and others suggested, as it seem enough reliable and stable to be used efficiently. I will probably use newsgroups again later if and when i will have more specific issue, in the meanwhile i go back to links you have provided me to read faqs for pgsql and npgsql. Thanks everybody for your help and suggestions.
