Ever since the 2.16 update of Defraggler on my WinXP Pro Sp3 the defragging effort is always incomplete by about a gigabyte, whereas the windows Disk Defragmenter leaves no scraps unfinished. For that reason I do not consider buying the Pro version.
Pro version does not defrag any differently to the free version.
What options do you run it with, in particular, do you Stop VSS, Exclude hibernation and Exclude restore point file ?
mta is tottaly right. the pro version is the same or at least almost the same as the free version.
And about the 1 GB left, well, i thingh mta is right again. check those options he mentioned and i thing you will be ok. at least i do select those options and everithyng works great for me.
Cheers