My netbook was having huge audio lag and just abnormally slow processing. After doing some searching on the internet, I found out that I needed to uninstall/reinstall the Primary IDE Channel found under the IDE controller section in the Device Manager. I would then set the Transfer Mode to DMA if available and everything would be great. For a period of time, I would see that "Ultra DMA Mode 5" was the current transfer mode, but every so often, it'd revert back to "PIO Mode", which is when it's really laggy.
What can I do to prevent the Primary IDE Channel to revert from Ultra DMA Mode to PIO Mode? Also, my netbook has BSODed a few times when it is in PIO Mode, without any real explanation.
I have a Samsung N120. Specs are as follows: http://www.samsung.com/ca/consumer/office/mobile-computing/netbook/NP-N120-KA01CA/index.idx?pagetype=prd_detail&tab=spec&fullspec=F. Only difference is that I have upgraded to 2.0 GB of DDR2 RAM.
EDIT: For all who are looking for an answer to this problem, click the link in Kythos's answer and look at number 6 (Re-enable DMA using the Registry Editor). This always works for me now. If on reboot, you seem to only have a black screen after XP is loading, just wait... it is still loading and will show signs of life after 2-3 minutes.