You might just want to call your ISP, the ISP knows what to expect from the customer's line. But if the PadI and PADo packets dont come through from the new machine it it not going to make through the inner loop to the CO.
Plus, the new machine will ne required to conform with the PPPoE standard (reference: RFC 2516) by lowering the MTU to 1492, because of the 8 Byte PPPoE header which has to come out of the MSS payload of 1460.
1460 - 8 = 1452, add 20 Bytes for the TCP header and 20 for the IP header, for a MTU of 1492. All the DSL routers in the market now have the configuration setting to accomplish this.
If you have any difficulty with the technical config. stuff your best bet would be to call your ISP's tech support, they will walk you thru it in no time.