BIOS Flash.What to look for?

I have a PC with intel i810 chip.As far as sound is concerned it works fine,but when i connect to the internet,the microphone stops working,or rather works but only producing a sound like a motor running,(It sounds like the recorded sound its been played back in a slower speed than the recording.)
I run windows 98 SE ,and my modem is internal.
The drivers are the latest and the only suggestion i got from the people who make the PC is to update my bios and see what happens.I have never flasheda BIOS before but according to the instuctions it seems pretty easy.Are there any points I should be more carefull about?