As already mentioned, don't use peroxide on wounds. Truthfully, it should be reserved for puncture wounds.
Pictures would definitely help, but basic care for wounds includes keeping it clean by using a product designed to be used on wounds --betadine, chlorhexidine or other wound wash--and apply a simple triple antibiotic ointment. Bandaging or covering will depend on location, size and type of wound. You want to concentrate on keeping it clean and using products that are not going to slow wound healing by damaging healing tissues.
Even if you can't afford to take this horse to the vet, you should at least call your vet. He may be able to give you advice over the phone based upon your description of the wound.
A good basic article: http://www.thehorse.com/pdf/factshee...wound-care.pdf