hi
on which links u want to have load balancing ??
whts the destination network ? if any ? and how its connected to ur routers ?
ru speaking about load balancing between ur router in ur local lan itself ?
then i would suggest to give a try for GLBP feature which will afford both balancing and reduandcy .
for more on tht just hv a look on this link..
again in tht case only 2 of ur ethernet would be used one from each router.
http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a00801541c8.html
if i m in ur place i would better do proper reading and get myself prepared to face the wrost before getting into implementing the same..
regds