Connection To Shared Drive Lost Over Wireless

My problem: Shared network drive (folder), when accessed over wireless from more than 1 PC (2 or 3) simultaneously, drops everywhere with a "The specified network name is no longer available" (in Windows Explorer), or "File cannot be read" (in a program). And I don't mean accessing the same file; yes, the files I've tried with are in the same folder, but when the connection is lost a)one client is streaming video from one file and b)another client is copying over some other file to the same folder. It even happens, for example, when one client is transferring a file, and another tries to list the folder. The connection for the file transfer is immediately lost.

My setup: Home network. 4 clients (3 laptops - 2 running XP and one running windows 7, and a desktop, running windows XP). 1 server, running windows server 2003 Enterprise Edition, 2Gb RAM, 2.66 Celeron CPU, and with a 1.3 TB Shared drive partition. The idea is to use the server as a NAS. The desktop and the server are connected via 100MBit UTP/Ethernet, to a DLINK DI-604 Router (WAN port of the router used for Internet). To another one of the LAN ports is connected a Wireless router, NETGEAR WGT624 v3. Wireless connection for the laptops is established at 54 Mbits. The share is mainly used for movies and music sharing between the PCs. When using the shared drive from the desktop (or if I use a LAN cable to plug directly to the DI) I have zero connection problems. For the wireless, however, as I mentioned before, the second I do two twings on two different machines that are connected over wireless simultaneously (and I've tried *all* combinations) the connection is lost for 5 seconds, which is not significant, but enough to be annoying if watching a movie or trying to use the "robust" file transfer of Windows.

What I've tried so far: Perfmon was showing that Page Reads were high, so I upgraded the RAM TO 2Gb(previously the server had only 1Gb or RAM). I tried having each client map the drive using its own account, that did not work either. I've been dealing with shared drives a lot (on win 2000-win 2008 servers), but not nearly as bad of behavior. Worst I've had is having to remap the drives every once in a while if not used or a client gets restarted and loses the mapping. However, I've dealt primarily with sharing over Ethernet, and not WiFi. I'm not a rookie by any means (I've covered CCNA and have done quite a bit of sys admin work as a hobby) I've done all of the basic troubleshooting, the problem is very specific and not a general networking problem by any means.