Comment 25 for bug 301958

I am a total Linux newbie, having just installed Ubuntu 9.04 on an Acer Aspire 3000 laptop which is having serious issues running Windows XP. It has an SIS graphics chipset. The display of Ubuntu on the laptop is terrible!
I have downloaded and applied "xorg-driver-sis671_0.9_i386.deb" (it tells me the package is already applied, or something).
To illustrate the problem I took a screenshot on the laptop, transferred it to my desktop (running Windows XP Pro). To my surprise, the screenshot looks perfect!
The attached picture shows my desktop PC displaying the screenshot saved on the laptop next to it. The laptop shows its usual Ubuntu picture. Clearly there is a major difference! The laptop seems to only be displaying a few colours and has a constantly scrolling horizontal flicker.
Any ideas? I would be most grateful for any assistance.