Help yourself to the backgrounds, whatever they may be. Simply right click on the name of the wallpaper you want then select 'save as'.

Sonic Adventure DX (2003)

Preview	Background	WxH	Type	Size
	Official Artwork: Gamma (E-102)	1280 x 1024	JPEG	252Kb
	Official Artwork: Knuckles #1	1024 x 768	JPEG	368Kb
	Official Artwork: Knuckles #2	1280 x 1024	JPEG	240Kb
	Perfect Chaos	800 x 600	JPEG	78.2Kb