check you have nodejs 0.10.x:

$ node --version
v0.10.3

If not, find package for your system or proceed to http://nodejs.org/download/

You'll need following repos:

git clone https://github.com/katuma/bitcoinjs-gui.git --recursive
git clone https://github.com/katuma/bitcoinjs-server.git
git clone https://github.com/katuma/node-bitcoin-exit.git
git clone https://github.com/katuma/node-leveldb.git

Installing the server (a bit convoluted to be able edit things in-place):

cd node-leveldb
git checkout dev/update_0.10
npm install coffee-script
cd ../bitcoinjs-server
npm install ../node-leveldb
npm install .
cd ../node-bitcoin-exit
mkdir node_modules
ln -s ../../bitcoinjs-server node_modules/bitcoinjs
ln -s ../bitcoinjs-gui public
npm install .
node server.js --bchdbg --testnet

Add to ~/.bitcoinjs/testnet/settings.js:

cfg.verifyScripts = false;

(Bitcoinjs is not capable enough to verify odd testnet scripts).