How can I access a bitcoind instance from another device with wallet functionality? I'm running bitcoind 7x24 on a linux host on my network so it is always in synch.

Options like:

  -rpcuser=&lt;user&gt;        Username for JSON-RPC connections
  -rpcpassword=&lt;pw&gt;      Password for JSON-RPC connections


suggest it is possible to have a wallet client on my Windows PC access that server and operate the wallet.dat on the Linux PC.

But my attempts have not met with success.  Can you suggest a solution or at least help me understand why this is not possible.
I have seen selfmade PHP frontends. May check google, forums, github or other sources. (want to avoid to post links there).

To answer the question properly: You can access the bitcoind instance through the RPC and do all kind of things. This indeed allows to use existing or selfmade frontends.

For reference on bitocin RPC check the popular forums or google up "bitcoin rpc commands"

If you intend a connection between a private server and you home server you could secure the copnnection additionally with a VPN for example.