guys you all need some reading to do...these things are so simple.
Any CYTA DSL Modem with antenna can have Wifi Enabled + Firewall + Security...
The reason of CRASHING... ( first of all lets not call this CRASHING but DISCONNECTING... ) could be the following:
Frequency Jamming... switch to different channel... everyone is using channel 11 these days, if 2 routers with same channel in close proximity you will have a nightmare. Also some old analogue devices such as cordless phones, radio nannies, wireless TV signal transmitters can really screw up your connection... Since Cyprus buildings mostly built of thick concrete & metal your signal really doesn't travel that far. And another issue... you have people leaching your Wifi if its unsecure, depending on your router setting...anytime who connects on your network will automaticaly kick your session out. So, get a 100Eur wirelss router such as 3Com, Buffalo, DLink etc and set it up using easy wizards.