Limited or no connectivity when connecting to a wireless router

I have an intermittent problem that is driving me nuts! I am using Vista
Home Premium on a Dell 1501 with an internal wireless card. My router is on
a pc running XP. The router is a linksys WRT55AG running 802.11g. All of my
other computers have no problem connecting to the router through wireless.
The vista machine goes into this fit 80% of the time where I get the infamous
yellow triangle telling me I have limited or no connectivity and I can not
access internet (Local only - whatever that means). I went to Microsoft help
page and found out that the power saving feature messes things up and since
then I am running at high power so that's not the issue. It does not matter
where the computer is. Even if I am sitting right next to the router, it
still does not connect to internet. 20% of the time it starts right up (like
right now) and I get the little earth thing on the taskbar and I can get to
the internet. Dell of couse said it is a Vista issue and I am sure Microsoft
will tell me it is a Dell issue. There is nothing wrong with the wireless
card and I have run all kinds of diagnostics on it and it has the latest
driver. Any help or insight will be appreciated.