Vector Ressing and total GUI failures

I am having issues with my graphics display. This seems to occur in three stages during the course of 15-20 minutes: (Warning: the images included are taken at 1900x1144 resolution and are, consequently, quite large :/ sorry about that)

Stage 1: World res's correctly, but Vector objects have the 'collapsed starburst' effect' ( http://www.shadowrequiem.com/SL/stage1.jpg )

Stage 2: Discoloration 'scramble' covers some textures, including avatar. ( http://www.shadowrequiem.com/SL/stage2.JPG )

Stage 3: Scramble spreads to GUI elements, making them unreadable.
( http://www.shadowrequiem.com/SL/stage3.JPG )

Can anyone suggest a possible reason for this?

System specs:
Windows XP
2.2 Ghz CPU
ATI Radeon X850 series
1.5 GB RAM
plenty of free disk space

It's your graphics card and ATI's drivers that get worse with every single release. Did you update to Catalyst 9.4?

First and to say it politely , your card is not the very best to use with SL.

Secondly, ATI broke their OpenGL implementation with introduction of Catalyst 7.12 and it's getting worse ever since then. You may want to try to downgrade your drivers to 7.11 (if your card is supported by these what I think) or look for 3rd party DNA drivers that backport to OpenGL from 7.11. Please also disable VBO in graphic settings.

Thirdly, I'd suggest you look out for a cheap Nvidia card like a 8600GT which should solve all your problems once and for all .