That is a more reasonable thing to ask XAMPP to do.
You still have some issues to surmount, primarily the problem of 'standard routers' and the number of available IP'S.
You need two IP's that can talk on Port 80 (for 'public' networks) - most routers can't do that.
One possible solution is an intelligent 'content router' that actually can inspect the headers and redirect traffic to ports. This would require very considerable effort, as you would need Cisco IOS programming (I suppose meaning you would have to learn it) Another is a programmable Dual WAN router, but you would have to look closely to see if it met your needs. Another would be to use a third machine as an Apache proxy, to redirect the IP's.
OR two cable/DSL/whatever connections and at least one machine with two NIC's
OR just a single bigger, badder machine. There are definitely limits on how much you can scale XAMPP on Windows Desktop OS's - mostly due to the Windows desktop TCP/IP stack which isn't designed to be used as a server !/O device.
You should try to use the right terminology - load-balancing is very specific and really only means methods to improve redundancy or increase available bandwidth for a single channel/object (the channel could be a server (or cluster), a network device, a disk drive (typically am array of drives))... http://en.wikipedia.org/wiki/Load_balan ... mputing%29
You meant what you said the second time, so... that's what you should have said the first time