h.323 client application thru gatekeeper

Hi everyone,
I expect that this works. This forum is my last hope. I was trying to make microsoft’s netmeeting work with the ip pbx of avaya communications. But the gatekeeper of the pbx refuses to authenticate the netmeeting client.After spending lots of hours into this, i thought of some other option. I installed the java phone by ibm and made it talk to ip hard phones connected to the pbx. But in this case , the java phone application doesnt go thru the gatekeeper, it just seizes an ip trunk and establishes a voice path with the ip hard phones. I am looking for a free h.323 client software which goes thru the gatekeeper i.e the RAS by the gatekeeper should admit this client. I searched a lot on net but didnt find any free client for windows. If any one can help me with either with the netmeeting thing or suggest me another h.323 client which i can load on my windows pc, so that i can make it talk to ip hard phones or for that matter digital phones thru the pbx, i would be obliged.please guys……