As a previous poster said, why aren't you focusing on truing your current wheels? If your current rims are rusted badly, or somehow damaged then by all means replace them. If they are "warped" (out of true) as you say then correct this by truing them. The spokes can apply all the all the force you need to straighten out the rim. If you install a new rim on your bike it will need to be trued. If you simply install the spokes and tighten everything up without paying attention, guess what? Your new rim will be "warped" too. This doesn't mean that you should return it as damaged goods! You simply need to adjust spoke tension to get things running straight.