Bicycle Tutor

I've just received a brand new back rim with a coaster brake hub for my birthday to replace my slightly bent freewheeled rim... This bike is basically an older road bike i've converted into a single speed. I'm just learning the bike game, so bear with me...
When i tried sliding the axle into the dropouts, i noticed that i have about 1/2 inch between the inside of the dropouts to the lock nuts on the hub on each side. basically i'd be bending the dropout portion of the frame inward just to tighten the nuts, which doesn't seem correct. can i fix this simply by putting 2-3 washers on each side between the dropouts and the hub locknuts or is there special hardware i should be investigating?
Any help would be appreciated. Thanks.

This is to be expected, road bikes have a drop out spacing of 130mm (older: 126mm or less), bikes with internal gear hubs have 120mm (as far as I remember). I'd use washers to fix that. However: be sure that the axle still protudes from these washers so that you can position the wheel in the rear drop outs. If you have a solid axle, it should also protrude from the frame so that you can still savely tighten the axle nuts. If it is an old road bike (steel frame) I'd have no problems "bending" it slightly (install the wheel with only a few / no washers).
I'd not only use washers but also a nut to hold the washers in position so you don't lose them when fixing a flat on the road. Just make sure that the outer diameter of the nut is about the same as the lock nut, just use the lock nut from your old wheel.
Other possibility:
- change the drop out spacing http://sheldonbrown.com/frame-spacing.html
- replace the axle (if it is too short). You have to know what you are doing there, if unsure, don't do it.
The other way round (hub wider than frame) is more frustrating, so I guess you're lucky.