Actually it's not needed to patch the ROM because of the auto patch feature in Zsnes and Snes9x. To take advantage of this function rename the .ips like the ROM's name or the zip if it's compressed, then place it on the same folder as the ROM or on the sram one you previously selected. Of course keep the ips extension, just make sure the name matches. For example:
Super Castlevania IV (U) [!].zip -> ROM file, if it's zipped
Super Castlevania IV (U) [!].ips -> ips patch (translation), on the same or on the sram folder
It works perfectly with Snes9x or Zsnes, but in the last one you need to enable the auto patch feature on the "Config" -> "Options" menu.
Also some translations need a valid header as alcotjez said, but a few won't work with it, so some times you'll need to remove the header if exist. The best way to know it it's reading each translation documentation.