extending wifi coverage with a second router best answer will be awarded?

I have a service provider router/modem not sure which it is... it cable from cable in and a wan line out.... the wan line out is plugged into a netgear wrg614 as my primary wifi router.... coverage was spotty upstairs so i bought a lynksis wrt54g... turned off dchp in the settings plugged it in lan to lan with the netgear and positioned it upstairs.... and plugged a xbox into another of the lan lines.... (xbox has interet access).... my problem is some devices will connect through wifi to one router or the other and only that on router.... some devices to niether.... and some to both.... (side note all device will connect to both routers but only to the internet on one or the other) my desktop which i connect back to the lan port on th netgear will not connect at all now.... and whenever i have a power surge or unplug the lynksis i have no connection at all until i reset the lynksis and resave the settings...even though they still show up the same in the settings menu..... anyone who can give a step by step idoit guide to setting it up right please help... thank best answer will be given