Some players meant for the S60v3 also works on 5800 XM, but they don’t have hardware acceleration, therefore video playback is extremely slow. Next major release of the popular
CoreCodec Core Player will support DivX with hardware acceleration on 5800 XM. Wait a while for them to relase it and then few more days for someone to crack it...

Till then you'll have to convert your videos to WMV/RV/MP4/3GP formats.
I'll post here as soon as I come across a HW accelerated DivX player