Ecoboy, what I did for filesystems is base off of the Windows file system method. So I have CD and DIR. OS DEV WIKI has some good references to the FAT filesystem (the main series has good ones too).
For sound, I would look into PCI first. It is actually fairly simple. There are only two registers for PCI and they are simple to use. The problem with sound cards is that they are often not standardized. That's why they come with driver cds. You might be able to figure out how it works on your computer but you would be throwing away portability. Contact the card's manager if you want details.
PCI is also a good way to get 100% control of the video card. VGA is great and easy, but it limits you to low resolutions and few colours. If you can figure out your graphics (they are less standardized than the Sound card), you can have graphics just like Windows.
If you haven't already, look into PCI. You can use it to access almost all deivces from Ethernet cards to Video Cards to USB. USB is also interesting but painfully long. The 2.0 specification is 600 pages long. On top of that there are the 3 interfaces that you need to implement.
On the topic of graphics, when will the next Graphics tutorial come out? It has been almost a year. HAVE FUN
