It certainly is possible using Windows98 and a good old fashioned dial-up modem set to auto answer incoming calls (and then you need some routing software to route your incoming requests out to the internet via your ADSL)
Needed a bit of research to get it going though - and it ties up your home phone line.
Probably better to find a dial-up ISP who has a geographical dial in number - BT used to have an 0121 number, originally published so that you could use dial up internet from abroad - but it also worked from with the UK.
Line One:- Zen Home 500 - DrayTek Vigor 2600VG
Line Two:- currently Nildam, but looking for a new home - DrayTek Vigor 2600