Those looking to blog via a PocketPC need look no further than moBlog.
moBlog is a .NET Compact Framework (.NETCF) 2.0 dependent application. Hence you will need to have .NETCF 2.0, which is a free download from Microsoft installed on your device. You can download .NETCF 2.0 here. It will work on any Windows Mobile 2003 / Windows Mobile 5.0 (WM5) / Windows Mobile 6.0 (WM6) devices.
moBlog currently supports Blogger, WordPress.com and Live Spaces with support for LiveJournal and MovableType/TypePad in the works.