Please note: There are two types of this board: (i) Non- Refresh Board (old) (ii) Refresh Board (there is a letter 'R' at the end of the sku)
Apparently, your one seems to be a non-refresh board as there is no letter 'R' at the end of the sku code. If your board is non-refresh version, it is compatible with only 65nm cpus from the list not 45nm cpus. So please make sure you double check before getting a cpu.
How to check if your motherboard is compatible with the 45nm cpu?
I think 5300 processors are supported. Basically 65 nm processors should work, they only say it is incompatible with 45 nm processors. Also on the top of the page you are refering to they say "not all boards are compatible with 5400 and 5200 processors" - both those series are 45 nm, Quad Core and Dual Core. But 5300 series is Quad Core on 65 nm and it should work.