as an attempt to work wireless network without network cards, I have the following configuration:

Cable modem-> Router1's uplink
Router1 connects to Computer1 and Router2 (Router2's Lan1 to Router1's Lan2 port) Router2 is Dlink's DI-624
Router2 connects wirelessly to Computer2
Computer2 uses a wired card with a wireless bridge (Dlink DWL-G810; "Infastructure Mode" ) connected to it

(it's not WiFi, but my priority is not to use a wireless card due to the too frequent reinstalling of OS)

Router2's settings are as par from the guide in tom's networking (Solution 1):
How To: Setting up File and Printer sharing between two routers

Computer2 can surf and transfer files (the ones tested are <1MB) through the wireless connection
but large files (~398MB) causes the Router2 to have wireless disconnects (cannot ping [persistent time out from ping] the router from wireless; and cannot ping Computer2[wireless] from Computer1[wired]) I can still admin router2 through wired connection from Computer1 at all times

the wireless disconnection persists until the message window popped up saying the network path is not found (immediately after the window popped up the connection resumes)

Anyone has any ideas on where the problem is and how to fix it?