It seems that, unlike previous years, window replacement can't be deducted in any way under home improvement or home repairs. Is this true? Or am I missing something?
The only thing that you can do is to add the cost to the cost basis of your home. That will reduce the gain at sale time, and any tax if any is due at that time.
A deduction is allowed for repairs to a rental property that you are paid to allow someone else to occupy.
If the windows needed replacement due to a casualty, you can deduct the casualty loss.
An improvement to any real property, whether to property you occupy or to rental property, increases your "basis" in that property. This can be deducted from the selling price, if and when you eventually sell (or dispose of) the property (and calculate the capital gains tax), but not until then.
Other than certain energy efficient improvements, home repairs and generally home improvements are not deductible and never have been.
Sorry, nothing for 2008.