Ok, my drive (Maxtor ATA133 40Gig HDD) is "stuck" on UDMA2 and it WILL NOT go any higher, it will go lower...(ugh) but nothing available over mode 2.

Open terminal.

su - root
**************

hdparm /dev/hda - to see what's up
hdparm -i /dev/hda - to see more of what's up

First I did this:
hdparm -c3 /dev/hda - it took it, and no problems. (Was on 16-bit...ugh.)
hdparm -d1 - that was already flagged, so no probs there.
hdparm -X68 /dev/hda - says its changing it...it doesn't.
hdparm -X67 /dev/hda - says its changing it...it doesn't.
hdparm -X65 /dev/hda - says its changing it...it DOES.
hdparm -X64 /dev/hda - says its changing it...it DOES.

Also tried a variation:
hdparm -Xudma5 /dev/hda - says its changing it...it doesn't.
And so on, and so fourth.

My bios (Asus A7N8X Delux) is setup properly.
My drive itself is setup properly.

Copy and past of hdparm /dev/hda:
/dev/hda:
multcount = 16 (on)
IO_support = 3 (32-bit w/sync)
unmaskirq = 0 (off)
using_dma = 1 (on)
keepsettings = 0 (off)
readonly = 0 (off)
readahead = 8 (on)
geometry = 4866/255/63, sectors = 78177792, start = 0

Copy and paste of hdparm -i /dev/hda
Model=MAXTOR 6L040L2, FwRev=A93.0500, SerialNo=662210832867
Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
RawCHS=16383/16/63, TrkSize=32256, SectSize=21298, ECCbytes=4
BuffType=DualPortCache, BuffSize=1819kB, MaxMultSect=16, MultSect=16
CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=78177792
IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
PIO modes: pio0 pio1 pio2 pio3 pio4
DMA modes: mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 *udma2 udma3 udma4 udma5 udma6
AdvancedPM=no WriteCache=enabled
Drive conforms to: ATA/ATAPI-5 T13 1321D revision 1: 1 2 3 4 5

Any ideas?

Exactly the same problem here on Mandrake 9.1 (WD 120 GB disk). Anyone found any solution to this?

I think I found the solution. You just have to add
ide0=ata66
into the kernel parameters (file /etc/lilo.conf, the append section at the data about kernel images) and then run lilo (both as a superuser) and then reboot.

Same issue, but ide=ata66 is in /boot/grub/grub.conf, I'm using grub, I've tried tweaking with hdparm with no improvement. Am I stuck at 28megs due to the fact that my hdd is spinning at 5400rpm? The hard drive is ata100 as well at the motherboard. I'm running an athalon 1.3GHz on a msi k7t266 pro2, but at work I'm running nearly the same setup (RH 9), but on a P4, and there I get almost 40 megs (but maybe the hdd is spinning at 7200, I'll check when I get there). Do i need to recompile my kernal for the Atholon or does RH pick the propper kernel on install?

Try ide0=ata66
(note the 0)

checked, I made a typo, I have ide0=ata66. Hopping that was the prob. I'm very upset at the slow speed. Seems like 28 vs. 40 something at work is due to rpms (5400 vs 7200). What was the use of getting an ata100 when its as fast as my ata66, the mobo supports ata100. I've given up and am going to just live with it.

You may need to download either the 2.4.21 kernel or download nvidia's nforce2 package.