TDS Exemption for certain vendors(Issue is urgent)

HI SAPIENTS

our client requirement is some vendors having exemption in TDS rates.they wanted to have One tax rate for all vendors irrespective of exemption rate.Can we have One tax code at the rate of 2% for example and can we control the exempted customers having less tax tax rate say 1% through the assigning the exemption reason in the vendor master record and the lower rate in customization for those vendors who are having lower rate.in this regard we can reduce number of tax rates for the client.i have tried it but it was not calculated with reduced rate.i expect somebody can throgh some light on these issues(the procedure&customisation)

Raja