Is it safe to run Windows and Ubuntu together on one PC?
Will it "mess with" my computer? I'm using Windows 7. Thanks!
Regardless of whether you use Wubi or set up a separate partition, your Windows install should remain safe. As with any major system change though, you may want to backup any data from Windows you consider important before proceeding, and ensure you fully understand what you are doing at every step of the install process.
If you have any further questions once you begin, please don't hesitate to search this site or the Ubuntu Forums for additional help. If you can't find a similar issue someone else had, then go ahead and post a new question. We're here to help!
Wubi is safe - I haven't seen a single case where installing with Wubi has destroyed windows. Back when 10.04 was released there were some accidental bootsector issues due to grub updates but those have been long fixed now. Wubi is much safer than installing as a dual boot as Wubi does not modify any partitions. That said, partitioning is pretty safe too, but there is a small room for user error when installing a normal dual boot - and letting Ubuntu split the partition of a Win7 or Vista install is known to cause boot issues - have a Windows repair CD handy just in case.
You should have a backup regardless of which OS you are running. That includes the ability to restore the OS, as well as safeguard your data. If you don't have the ability to do a full restore you're asking for trouble as hard disks can fail.
Summary - Wubi is a safe and convenient way to try out Ubuntu. Especially if you later decide you want to remove Ubuntu: it's as simple as going to Control Panel, Add/Remove and double-clicking "Ubuntu". If you want a long term, permanent Ubuntu install it's better to partition.