You can always send a note to the project leaders, I'm sure they will appreciate it. As it happens, an error by the PHP group in 5.3.7 has thrown a spanner in the works, invalidating the work of all the people developing suite distributions. I'm sure the latest version is critical to your development work, so I'll tell them all to toddle along more quickly.
In the mean time, here is why (while you are welcome to try) you probably can't upgrade individual components of XAMPP.http://bravo.newnetenterprises.com/word ... stallation
The technical explanation would be that in XAMPP, Apache and PHP are co-compiles.