Hi zgnilek, and welcome to the vista forums,
It seems that you have tried most of what I would suggest, some other things you may want to try ...
Disable IPv6 in NIC properties
Check router manufacturer for Vista firmware updates.
you don't say which browser you are using but have you tried an alternative to check if the issue is browser related.
Have seen a fair amount of discussion of this sort of thing with vista - not common but definitely a problem with some set-ups which is not at present been solved but strangely quite often cures itself
