Are you sure you have selected the correct model here? If so, there is nothing special with this series that prevents you from using other brands.
While it's a bit of work, the HD you do put in must be a SATA II (3.0 Gb/s) drive (or one that can run at this I/O speed). Review this IFIXIT guide: iMac Intel 24" EMC 2134 and 2211 Hard Drive Replacement.
You may want to give your system some kick here by installing a SSHD unit this is a hybrid drive that has a SSD for speed and has a traditional HD for storage. Seagate makes a nice one and they have some very large drives too! Heres the details: Seagate Desktop SSHD. These drives auto sense the SATA ports speed and sets its self to it.
You do want to make sure your systems firmware is up to date as well review this Apple TN: EFI and SMC firmware updates for Intel-based Macs before you do you anything.