I recommend you leave the bios alone. Epox has been out of the board business for awhile, though someone may be using their name on other boards. If you can't find an epox approved bios flash program on their website, the using another bios flash program will leave you with a dead motherboard. Been there, done that. If the system is running now, count your blessings. That's a very old board and the fact that it still works is somewhat amazing. If you want to run a newer cpu, save for a board/cpu/ram upgrade and list a budget for recommendations.
Updating the bios won't permit you to use windows 7. If windows 7 can find device drivers for your board, it will do so without the bios flash. The bios flash only effects hardware on the board, not software. If it can't find the lan driver, use an old lan card, which has a generic driver. If the lan is connected and you can get online, then let windows 7 search for updates. If it can't find the proper driver, then you'll have to settle for partial drivers. The board is too old.