Most of us probably know how hard it is to upgrade firmware. Luckily, Lewishamilton and Stiffmeister have created an application that should simplify the process of upgrading your PSP.
They've developed the first 3.90 M33 Easy Installer program for the PSP, which should allow you to upgrade to 3.90 M33 on Windows 2000, XP and Vista machines.

The main problem you might have with this installer is the fact that it's not completely in English. That being said, if you want to activate the installation procedure on your PSP, just select the drive letter that corresponds to your PSP, and then click on "Installeren." That should get everything up and running.

As for what the developers have to say, here's a quote from our forums:

This version is still in development stage. But comes very rapidly v2 with kernel and sits there nicely. Then no longer goes that by means of winrar.

As the malignant and lite kernel ends up we let us do that also.

In any case, for those of you who want a relatively quick and painless process for upgrading your firmware, then you may want to try this out. Enjoy!