Today Apple released 10.5.3 as an update available through Software Update. If you have vanilla kernel, just go for Software Update and enjoy 10.5.3 after downloading of about 400mb (depending on your hardware). For everybody else it will be tricky to get it work before somebody makes a .dmg for your distro. Many sources report that it is safe to install this update even on a hacked kernel. So if you have a well working hack with ToH kernel 9.2.0 or 9.2.2 you can try to update manually. This guide was made for 10.5.2 but apparently it works with 10.5.3 too. Guide can be found on Netkas blog
Apple Combo Update can be found here: 10.5.3- 536 mb
If you don't want to do it yourself, wait for somebody to release .dmg for your distro and stay tuned!
