I just bought a new laptop, and right now I’m using Windows. However, down the line I would like to dual-boot Linux as well. If I’m going to do that, can I just buy the “one year, one computer” version? Or will that not work? Will I have to install twice? A Windows and a Linux version?
Please excuse my lack of knowledge, I’m a first time Linux user.
Generally, it’s possible a dual boot Windows and Linux.
Some laptops (most of them), come with a recovery partition that is necessary to recover the computer if anything goes wrong with Windows.
I suggest you got an expert friend to install a dual boot system for you.
Avast for Linux is a totally different product (and free for home users) to that you will require for Windows.
Which Linux distro you use will decide which avast package you install.
Try using ubuntu linux. 
They have this thing called wubi where you install and uninstall ubuntu as if it was a program.
It’s always a good idea to start a thread at your Linux Forum about something you’re not sure about.
Generally, if you’ve thought about it someone else has too, so to avoid getting some heat from the ‘Mods’ do a Search first ! 
Avast! does build what I think is one of the best Linux Anti Virus Tools, but honestly with the difference in Linux Distros, get all the info you can.
We can’t cover info on every Distro, obviously. Avast! for Linux will run on all Linux Distros however.
Also it’s really unlikely you would pickup a Linux Virus, as none have ever been made !!
But; what we are trying to stop is infecting your Windows Partition with a Windows Virus, from within your Linux partitions, plus infecting your Windows User friends.
When you install a Linux Distro, it installs a Bootloader, generally GRUB.
This controls a Boot screen giving options to Boot into Windows, or Linux, plus some more advanced options.
I know with my Distro this is so, and I happily used WinXP, and PCLinuxOS for 3 years, dual booting, no problems.
You want to backup yor Windows MBR (Master Boot Record) .
The Master Boot Record (MBR) is a small, dedicated section at the beginning of the hard disk which holds the boot information and partition layout for the whole disk. The MBR itself is only a single physical sector in length (512 bytes), but it is required in order to create or maintain partitions on the disk, or even boot the computer. The following describes the different sections of a valid MBR, which helps to explain the importance of the MBR.When any part of the MBR is missing or corrupt, the machine will not be able to boot.
You would delete the Linux Partitions from Windows, and Restore the MBR, if you weren’t happy Dual Booting.
Please seek specific info for your own Linux, and Windows Operating Systems.
I’ve only given a General overview.
Regards.