Oh, I thought you were running ubuntu on the bare metal - but actually
you're running a pc OS? Are you ubuntu in vmware inside microsoft
windows? That would explain a lot of the performance problems.

Or, if you're using "pc" in the sense of "pc-class hardware", I think I
remember your machine is low spec. I don't know of anyone else
downgrading X on ubuntu 10.04, especially since the version is not at
all the newest, but a rather conservative, older version.

Back in the days of ubuntu 9.04. which performed disastrously with intel
graphics and killed netbook performance, there were repositories set up
to downgrade to the older version of the intel X driver, which was much
better performance wise. Later, there were repositories available frm
which to upgrade to the newer version of the intel drivers, which was
even better.

But there have really been no such problems with the 10.04 X drivers, so
there has been no system set up to fix any such problems.

There may be some info on that, but I'd have to google for it. Chances
are it would be more trouble than doing a clean install of 8.04