AROS has no problem dual booting with win7, i have done that myself.
Rough procedure is
-Install win7 but leave some room on the drive that is free and unpartitioned. 5-10 GB should be plenty.
-Install AROS selecting the option "Use free space on drive" to maintain the windows partition.
-AROS will install GRUB, detect the win7 partition and create a boot entry in GRUB for win7 and AROS