RAM sizes over 512 MEGS under Win 9x/ME (ME is the most P.O.S. OS Microsoft ever wrote and it's a disater by itself, IMO) have been problematic. I'd reduce the RAM to 512, don't use the USB sound card at all, make sure you have the latest drivers for the PCI card, and confirm you've got DMA enabled on your hard drive- for starters.
Then take a look at your IRQ's to see if the soundcard is on the same IRQ as the Video card. If it is, then move the sound card to a different slot until it is (ideally) by itself or at least not sharing the video card IRQ.
Let us know how you're doing after you do that stuff-