mmmmm... unless I misunderstanding your question, you want to know what chip you can put on a 486 board? The only way of taking that board to the pentium realm is to try to find one of the old 486 to pentium "Overdrive"(at least i think thats what the name was) chips. and thats just plain silly. You also might try to find an AMD 486/133. Those were some hardworking little chips and you could get them by the dozen. The only other thought is to build a new system, but salvage as much as possible.
If the case is an AT or babyAT case and not some namebrands useless case then you can reuse it($20-150 New). if the hard drive is at least 500MB then you could build a websurfing machine with it, but it will be slow and not have much life left. 4 meg video cards can be had for $30, but if needed that 1meg you have will show color. 8bit sound (wooooHOOO!) is better than no sound($15 for cheapo 16bit, $50 for very good card). pray it uses 72 pin sims(memory) and not 30. 30 pin sims are good for some sound cards and shiming your dining table level. if its got at least a 28.8 modem you can check email. Now you just need a CPU and Motherboard that will fit your case and work with your mem.