Demon, Vista, XP, Wired, Wi-fi and Lag

Ok.
Before anyone tells me 'It's because of Hallowe'en', I get this all the time.

'This', being unbearable, unplayable lag, never dropping below about a ping of 4k/s. It began a few months back after suffering only with lag to ~500ms, then it suddenly skyrocketed.
To that end, I've been experimenting. The laptop I run GW on dual boots Vista and XP, mostly Vista. At the same time, I directly plugged the laptop into the router, rather than, as I normally do, through the wi-fi.
Results:
Vista, Wireless: REDENGINED
Vista, Wired: ~500ms lag; only just about playable.
XP, Wireless: Even worse than Vista wireless. Couldn't even load up 3 of the 4 areas I tried.
XP, Wired: Perfect.

I have a problem with this, being stuck to the router is kinda irritating, a laptop's meant to be portable. The cable I'm using should also be connected to the printer - so nobody else in my house can print while I'm doing this.

And am also bemused as to how the wired/wireless connection affects it so drastically. At first, I figured that it was because the (And I apologise if I end up using the wrong term here) wireless network might not be able to 'take' the amount of packets GW sends out - but that makes no sense, as the WLAN's Bandwidth and connection speed is much greater than the outside one.

One final thing to add, is that my ISP is Demon, an ISP, I understand, others have had problems playing GW on. Changing ISP is effectively impossible, at least for the next twelve months.

Any details you need, just ask. I'm not the most handy with computers, but can do most things.
Thanks in advance.

I had the same problem on my pc a while ago. When I connected to the internet with my wireless, Guild wars would spike lag every 2 minutes. Tracked down my problem to wzc or wireless zero configuration service. It is a service that looks for avaible wireless networks even if you are already connected resulting in a spike lag.
In windows vista you cannot disable this service without losing your wireless connection.
In windows xp you can do this, however you cannot disable the service on startup cause you need it to connect to your network for the first time.
Here is how i did it in windows xp:

1) Startup windows xp and connect to your wireless
2)Start>Run : services.msc
3)look for the wireless zero configuration service, right click, Stop
4) play guild wars without spike lags

This procedure may be a bit tedious so here is a faster method:
1) create a new text file
2) put "C:\windows\system32\net.exe stop wzcsvc" in the text file
3) Save rename to stop.bat (make sure you can change extensions)

Next time you want to disable Wireless zero configuration just launch stop.bat

Hope this was helpfull

Try updating your router's firmware. It sounds a lot like a router issue.

Ok, I can think of a few things to check.

If you live in your own home or an apartment? (we do not need an answer)
as things that will/can screw with wireless:
-old vacuum cleaners(or any old large electrical motor)
-older cordless phones
-wireless thieves(someone stealing your internet connection)

other things to look at.
The age of the wireless card and router, specifically what it is rated for. Some older routers/wireless cards are slower than the wired connection. You need to check both the card and router.

Have you power cycled the router? turn it off or unplug it for 30 seconds? I often need to do this to my current setup (about 1 time every 2 weeks).

just a few things to consider/ look at.

What router/firmware are you using that you have to do that so often?