No you can't. You can have extended desktops and multi-monitor setups at different resolutions, but the actual eyefinity has to have the same screen resolution on each screen.
I stand corrected. From the Eyefinity FAQ:
Can I support different resolutions?
All monitors running in a Display Group or cloned modes must be running with the same resolution. If monitors have different native resolutions, the highest common non-native resolution between the monitors will be used when creating Display Groups. Monitors running in extended desktop mode can have independent resolutions.
Complete FAQ can be found at:http://www.amd.com/us/products/technologies/amd-eyefinity-technology/how-to/Pages/faqs.aspx