Just ordered the cpu for my motherboard: ASUS M2NBP-VM CSM: AMD Athlon 64 X2 5600+ Brisbane 2.9GHz 2 x 512KB L2 Cache Socket AM2 65W Dual-Core Processor. I hope it’s correct for the board. I`ve never installed a cpu before are there any tips or tricks. I.E. Will the bios see the new chip. I have a fan from the AMD 3800 will that be enough for the new cpu. Any tips would be greatly appreciated.
First off, yes, it is physically compatible with your board (65W AM2 part). You might need to update the BIOS if your current BIOS was created before the Brisbane parts came out. According to ASUS's website (http://usa.asus.com/product.aspx?P_ID=MnOfzTGd2KkwG0rF - click on the CPU Support List tab) you need BIOS version 1001.
If you need to upgrade your BIOS, you can download the BIOS and instructions from the first link I provided (on the Download tab).
As for the cooler, was your old CPU a dual-core or only a single-core 3800? If your 3800 was dual-core, you old cooler should be sufficient (they'd both be 65W parts). If you re-use the cooler, you will want to apply new thermal paste/grease.
If your old CPU was only a single-core, the old cooler might not be sufficient to cool your new dual-core CPU. If you bought a retail-version of the new CPU, it should have a cooler. If you bought OEM/bare/used, you might want to look into getting a new cooler just in case.
If you need help with the actual process, you can find many guides online.
Honestly, your old cooler will still work, but the temps might get a little warmer. Use software to monitor your temperatures (CoreTemp: http://www.alcpu.com/CoreTemp/). If the temps get a little warm (70-80C), just get a good heatsink, something like one of these (really, just check the reviews on newegg, there are many good heatsinks, these are just examples):