We're planning on moving to Exchange 2010 here in the near future, and I have what may be a silly question. I've read on MS site that the system requirements are Windows 2008 R2 Server Standard or Enterprise, would this exclude us from using DataCenter version?
No, Exchange does not exclude it. You can use the Datacenter version just fine. It's not officially supported, however. If you have a license for datacenter, you're allowed to downgrade your installation to Enterprise if you so choose. You're also allowed to run virtualized Enterprise/Standard licenses as VMs on a system with Datacenter license without additional license requirements.
Just make sure you're using at least 2008 x64 SP2 or 2008 R2.
Edit: added additional info
Edit 2: According to this Technet link, Exchange 2010 SP1 supports Datacenter edition. RTM Exchange 2010 does not seem to officially support it however, if you click the Exchange 2010 link on the right under More Resources.