Have a desktop with Windows Vista Home Premium 32bit installed. Presently, it has some corrupt files and can only be launched in safe mode. I write to inquire about Ubuntu as a back up installed. Microsoft says it is supported but I would ask if Ubuntu can be installed to a second hard drive in such a way as to allow booting to either operating system.
Next question would be on if Ubuntu will install to a separate partition and allow OS selection on bootup.
Lastly, this is an HP Pavillion a420n desktop... AMD Athlon 3000+ Processor with 512mb memory and a maximum of 2GB. Hard Drive is 160GB with 85GB free. No problem upgrading the memory if needed but I would ask what would be the appropriate Ubuntu install with this environment. I am aware of "Lubuntu" but would want an experienced consult.
People have been doing exactly what you describe for many many years. There are plenty of guides out there for doing this as well, and quite probably some of them specific to Ubuntu are on the Ubuntu DVD.