This is a known problem with Windows 7 and TIF files. For a certain (legal) variation of the TIF format the built in image viewer in Windows 7 will show these lines.
Microsoft never cared to fix that problem with an update – however a Hotfix is available.http://support.microsoft.com/kb/2459492
An easier option is simply to use another image browser. I for my part use “Faststone Image Viewer” (freeware).http://www.faststone.org/FSViewerDetail.htm