There shouldn't be any problems with using Boot Camp and Parallels.
The partition size for Windows can be any size you want.
First you need a Windows 7 installation disk.
Then you run Boot Camp Assistant.app located in your Mac's Utilities folder which is in the Applications folder. It has an option to print the instructions. You may want to do that so you can refer to them while you're running Windows. You can also print them to a pdf file so you can read them on your computer. Tell Boot Camp Assistant to create a Windows partition. Select your Mac OS X disk. To create a Windows partition, Boot Camp will shrink the OS X partition. Once the Windows partition is created, Boot Camp will ask you to insert the Windows installation disk and will restart the computer to start the Windows installer.
In the Windows installer, you select the new partition which exists on the disk after the Mac partition and which has the size you specified when it was created.
After Windows is installed, the Mac will boot the Windows partition. Now you can install the Boot Camp drivers which are on the Mac OS X disc.
Once you have Windows working in Boot Camp, you can boot into Mac OS X to setup your Parallels virtual machine.
Go to the Parallels Desktop menu, select File -> New... -> Skip Detection -> Windows 7 -> Custom -> select Processors, select RAM -> Boot Camp Partition -> select the disk containing Windows 7 -> select the Networking type -> Virtual Machine -> select name and location (defaults are good).