It's called Astral Walking, and only two people on Earth in SR know how to do it. Good luck getting either of them to teach you.
Really only 2? I'd have thought most of the immortal elves and dragons would know if.
While the dragons and Immortal Elves can astral project, astral walking was a high level ability of a certain class or set of classes, IIRC. And there wasn't much in the way of multiclassing in Earthdawn.
As for the two who can do it, I believe Harlequin is one of the ones who can do it, and I forget who the other is.
The ability I think you're talking about is called Astral shift not Astral walking, it's a high level lightbearer ability. As for the two IE's that are thought to have been lightbearers that's Harlequin and Ehran if I remember correctly, though that does not mean they are the only ones knowing that ability.
There were other ways of physically entering Astral space in ED as well. The high level nethermancer spell spirit portal let you enter astral space as well and you could summon a spirit and have it use the astral portal ability, and yes it did let you enter astral space physically not only projecting as it is in SR, they go as far as to specifically say that it is one of the most common reasons for summoning spirits in the ED magic book.
As for near teleportation phenomena there is the high level illusion spell other place that let's you connect two doorways no more than maximum a mile apart, you can then travel instantly between the two due to a warping of astral space. Likewise the high level nethermancer spell gateway allowed the caster to open a gateway to a previously cast bone circle with a max range of 5000 miles.
On top of all this there were rare stable natural rifts that let you enter and exit to either the netherworlds or to astral space.
So clearly in ED it was not exactly uncommon to use one or more of these ways to enter Astral space and to perform some sort of teleportation like movement.
It would be pretty safe to assume to all of the IE's and GD's know at least one of these ways.
Oh and having multiple disciplines were actually fairly common and is covered in the crb.