"I unintentionally recorded in HDV mode on my Canon XH-A1 on DV tapes (instead of DV) and now cannot transfer the videos into any software I have. Is there a way of overriding the software? If not, which program will accept the HDV."
Most of the HDV footage I've seen from the XH-A1 looks amazing, so hopefully you'll be pleasantly pleased with your unintentional results. If you recorded in HDV mode then what's on your tape is HDV, not DV (the tape doesn't matter, the HDV and MiniDV tapes are the same with different packaging). HDV is reasonably mature as a format, with widespread support from most of the major video editing packages. Here are several options for capturing your HDV footage.
HDVSplit is a freeware application for capturing HDV from your camcorder. It's reliable and doesn't drop frames, but I've seen instances where the resulting footage isn't compatible with other editing applications.
Pinnacle Studio HD is an affordable alternative for editing HDV files. It includes all the necessary components for editing, plus the ability to do things like author Blu-ray disks from your footage.
Sony Vegas is currently my favorite solution for editing HDV footage. It offers subtle features like aspect ratio selection and clearly spells out the resolution of the preview window so you know that what you see in preview is not necessarily what you get. Sony Vegas is also a rock solid editing tool with all the bells and whistles of a full featured video editing tool.
Roxio Creator is a solid alternative for HDV capture and editing. The bundled video editing solution is easy to use, with an easy to navigate interface that will get you from camcorder to final product in the fewest steps. Roxio is currently the best value of the bunch with a 15% off coupon on Easy Media Creator and an additional 10% on all Roxio products using coupon code SAVE10ROX.
Nero also does HDV, although I find it lacking compared to the other offerings. The video editing components of Nero Ultra Edition still feel like they come second to other aspects of the Nero bundle like DVD burning and music management. Nero comes in as a close second in price to Roxio, which makes it a viable alternative if budget is an issue.