My wireless desktop doesnt keep a constant connection to the network?

I am using a linksys wireless G USB network adapter in conjunction with a linksys wireless g router. My PC goes through spells of perfect connection, but then will go a few days disconnecting me every few mintues or so, so times not being able to connect for an hour or so. The entire time it is picking up the network, just refuses to connect to it. I place my wireless laptop right next to it and the laptop stays connected the whole time. Also, over the last few days, my connection has been extremely sluggish even when i am connected, despite showing a "good" to "excellent" connection. I've had the wireless adapter for about two years now. do you think i need to go out and buy a new adapter or is the problem with my computer itself?