So to sum up my slightly complex append above you can do as follows (depending where you start):
To go from west to east. Start at Brindley place and the canals, go through the convention centre (look in at the symphony hall if it is open), come out into centenary square (ice rink), keep going straight ahead and through the new library, out in Chamberlain square (fountain), see the entrance to the museum and art gallery, then into Victoria square and the German market.
If you do it the other way round (east to west).
Start in Victoria square with German Market, walk past entrance to museum and art gallery, into Chamberlain square (fountain), under the new library, out into Centenary square (ice rink), go towards convention centre, go through it (looking in to symphony hall), out the other side of convention centre, cross canal by bridge into Brindley place.
The total walk is less than a mile, but it can easily take half a day or more depending how much you look at.
As I said, the walk either way is totally traffic free.
Here is a map that may help. The area I am discussing is on the left of the map. You can see Victoria Square Centenary Square and others things I mentionewd marked on the map.
You can just see the Hyatt hotel but the Convention Centre is just off the left of the map.
http://www.networkwestmidlands.com/Bus/Bham%20 City%20Centre%20June%2007.jpg