Hey Robbert, dont let these Overclocking Maniacs get ya down..
But a 486SX does need to be upgraded, but dont throw it away as mentioned earlier.. There are several things that I have done with older 486s that I have had in the past..
1) Get a faster 486 processor they took them all the way up to 100mhz and you can get one of those cheap.. But you will want to upgrade soon after you do this. (cheap fix)
2) Get a replacement motherboard with a pent 133, 166, or 200 on it.. If you check the for sale forums every once and awhile someone will have one, and will let it go for pretty cheap. ~20-30 or so.. You already have all the components you need (you may need some newer ram) but you have a Power supply/floppy/hard drive.. This is what I have done with most of my 486's..
I think I have a 486DX/2 66 Laying around here somewhere.. if you want it let me know I will send it to you, it is not much, but it will be faster than what you have in there now..
If you have any questions, either post here or email me..