How do you finally conect? By turning the routers power off and on? - If that is the case, you may have the wrong "Idle Timeout" setting (in Basic Settings of the router). Best is to set it to 0 (zero).
PS; I just see you have a Frtzbox. That damn thing is giving me all kinds of problems too on the wife's PC (but not the same as yours). I had to get the dongle because the integrated WiFi died.

Do you have the latest driver updates? Do you have the latest service pact for vista? http://support.microsoft.com/kb/956119/en-us

Very nice Link Rick! It says to pretty much install service pack 2 as well..

Thx, Rick, but I have SP2 and everything up to date. Believe me, this isn´t going to be an easy one to solve because I have tried EVERYTHING I can in the last 6 months or so and nothing helps, lol. Sometimes the connection just comes back by itself (after having WLAN enabled) but I can`t find out why. Matt

@Matt,
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Yeah, I hard address the machines and wifi router plus never use hibernate nor sleep so have not experienced the issue but it does seem to come up often.
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Best Regards,
Rick P.

LH, yeah it only happens after using hibernate!! Then I can do a restart and my connection is lost. I´ve also tried to a "hard" reset with various routers that I´ve had and that doesn´t help either!!
Rick, I´ve also tried giving my routers completely new ip adresses then using a static ip on my pc, this, sadly, also fails after hibernation!! I never had any problems occur whilst using XP and as you say this Vista problem seems to pop up quite often doing a google search.
What gets to me most of all is that I´m learning to be a network admin one day and I can´t even get this problem fixed, LOL. Cheers, Matt

Maybe I´m getting things confused, sleep, standby or hibernate, I thought they were all the same!! I power down the PC and can wake it up by either moving my mouse or pressing a key is what I meant

The power states used in ACPI are nicely summarized in this Wikipedia article. In common usage, sleep is ambiguous and should be avoided when possible. To be most specific, use the ACPI state designations, as many modern BIOS menus do.

S3 is now usually called "sleep", and used to be called "standby". S4 is "hibernation", though in Windows you can choose to put the system in S4 hibernation by pushing the "sleep" button. Also adding to the confusion is Windows "hybrid sleep" which puts the system in S3 sleep, but writes the S4 hibernation data to disk in case of a power failure. Microsoft explains the differences here.

The power management setting, "Allow the computer to turn off this device...", is not part of S3 sleep or S4 hibernation. This is, I believe, only a device power state, what the ACPI spec calls D0 through D3. This is used to remove or reduce power from one device while the entire system remains running (G0 state).

In S3 sleep, all devices except the RAM and what is needed to keep the RAM refreshed, should be powered off. In S4 hibernation, all devices must be powered off since the system is put into a G3 standby-power mode.

@Matt, are you referring to this old thread from 7 months ago? It seems like it was solved. Is this a new problem or the same one?

@LH, thanks for the compliment. You've been on fire today answering posts, so I had extra time to write all about power states. :-)