hi and welcome!
u currently use mirc to d/l stuff? first time i hear that u can use mirc to d/l stuff.
the ADSL limit is by your isp. there is a limit on ADSL Packages, you do get unlimited access though.
the cheapest at the moment is a 30GB Monthly Limit for R199/month(Just till 31 OCT 2005, dont know wats going to happen after that) by webafrica.
You will need to get a ADSL Line, you have the following options,
192 kb/s
384 kb/s
512 kb/s
And you will need an ISP, just like i mentioned above about webafrica.