Fortunately when you have a DSL problem you are fully supported by your DSL tech support as part of the monthly fee you pay them.
They should help you get the correct drivers for that older modem, or replace the modem with a Win7-capable one.
For example, every time I call Earthlink (about every 3-4 years) they offer to send me a newer, more advanced modem for free since I am their valued customer. Then they walk me through installing it.
Hope they treat you the same way. Let us know.