If my internet provider works on adsl1 and I buy adsl2+will it work or not?is adsl compatible to adsl1?will provider force me to get adsl1?

Backward compatible. What is ADSL/ADSL2/ADSL2+ ? (http://whirlpool.net.au/wiki/?tag=DSL_modemS01_02)

If your ISP provides ad ADSL 1 connection you CANNOT get ADSL 2 from them, quite simple really.

Please clarify your question.

I read between the lines as "If I bought a ADSL2 modem, woill it work on my provider's ADSL1 or would I have to buy a new modem"?

Lets' clarify the question a bit and also remind the original poster that the provider usually provides the modem as part of the service, generally if you keep if for a certain length a time, say a year.