HI Yakkob,
Yes this is possible - the Netgear router that Sky sends out is actually alright, but if you do want to use your own kit there are a number of resources on SkyUser & Google that can help you.
The ADSL user names are based on the MAC of the router which Sky sends you, but this won't stop you using your own router with it's own MAC, just as long as you use the user name dervied from the SkyBox MAC.
As for the password, this is most likely randomly generated, however it has been speculated that it is in some way derived from the MAC of the SkyBox via some kind of algorithm - however i can't see any real benefits to this.
Have a shot at some of the methods on SkyUser, and let us know how it goes.
Regards,
Justin
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SkyBroadband 8mbit (Connect Package)
Exchange - Bangor (N.Ireland) | Line Length (sight): 0.06km | Line Length (cable): 0.062km
Line Sync - Downstream: 8128kpbs | Upstream: 448kpbs
Attenuation - Downstream: 13db | Upstream: 7db
Margin - Downstream: 16db | Upstream: 29db