linux server as load-balanced gateway inside a network with 2 routers using only one network interface

[Georg Hohenberger <Georg@xxxxxxxxxxxxxxxxxxxxx>]

hi,
i am planing to use my linux-file-server as getway for the lan

this file-server has 3 network interfaces:
   Gigabit --> lan (switch)
   Gigabit --> my computer
   100Mbit --> lan (switch)

inside the lan there are two dsl router (my and my neighbours)

linux-file-server should do load-balancing using this routers to be the 
gateway to other pc in the lan and even do port-fowarding and qos 
(Quality of Service) for voice-over-ip

all this should be done over the 100mbit network interface

i would like to know if this is possible to do or not

ofcorse tips and hints would be great

thanks in advance

Georg form germany