So I purchased and played about 3/4 of Dawnguard not long after its PC release. I was having a great time and really enjoying it.

I however encountered a graphics bug during the quest to collect Auriels bow. I saved and reloaded but the bug persisted. I eventually managed to complete the Dawnguard storyline in the hope that this would fix the bug, it did not. Nor did the purchase of Hearthfire.

Completely re-installing the game does not fix my issues, nor does starting a new game or loading a previous save.

My system stats:
Intel Core i5 M460 @ 2.35GHz (quad core)
4Gb Ram
Win 7 64 bit (SP1)
ATI Mobility Radeon HD 5650 1Gb Graphics (with swtichable to intel onboard chipset) (Drivers are latest available from HP website (Version 8.771.1.0)

mod list: http://steamcommunity.com/sharedfiles/filedetails/?edit=true&id=107924480

Screenshots:

http://steamcommunity.com/sharedfiles/filedetails/?id=92844407
http://steamcommunity.com/sharedfiles/filedetails/?id=92844401

The bug is not present on my power saving graphics settings though performance is too poor to actually play the game.

EDIT: I have concluded that the glitch only effects larger areas, e.g I can be in whiterun and have no problems with my immediate area but the sky outside whiterun will be riddled with those stripes.