re DSL 3780 - no way to allocate fixed IP addresses or host names as per Netgear routers or the Huawei hg533 routers. I find this and lack of access to an advanced user setup manual a great big negative. The HG533 is much more preferable and unless the menu in the DSL 3780 is changed I really would like to go back to the HG533.
In the routing table (sometimes just labelled 'attached devices' in some routers) you have the option to change it from dynamic to static (drop down box in table) this 'fixes' any IP issued to the device by the router.
You should also be able to click on the MAC listed there and change this to a name in the same place, click submit to fix your changes.
I can't say I have tried inputting my own IP in the table, but this should work too, because the IP is fixed once set to static I have never felt the need to change from what the router has issued itself personally, but you should be able to set your own from the routing table as well one would assume...