Following this thread on TCPMP MP4 Can Be Played on Windows 95/98/ME! well ... the answer is : if you have the right CPU ! virtual machine is cheating 😉
But, what would be the lowest configuration to play 3GP video files ? We know it works with any P3 and 128 Mo with win98SE.

- 3gp (container) video : h263 audio : amr
http://techslides.com/demos/sample-videos/small.3gp
or more samples here http://samples.mplayerhq.hu/mobileVideo_3gp/
you can also ffmpeg -y -i <input.avi> -r 20 -s 352x288 -b 400k -acodec libfaac -strict experimental -ab 64k -ar 44100 -ac 2 <output.3gp>

- mp4 (container) video : H264 - MPEG-4 AVC (part 10) (avc1) audio : MPEG AAC Audio (mp4a)
http://techslides.com/demos/sample-videos/small.mp4

Some feedback ... with my good old acer travelmate 507DX equiped with a mendocino 466 MHz, Northbridge Intel i440MX rev. 01, Southbridge Intel 82443MX rev. 01, Memory (32 onboard + 64) 98 Mo, GPU neomagic 128xd driver 6.27.00Q, Crystal audio version 4.12.4021, DX8.1 and Win98SE
I was full of hope that TCPMP would play some xvid, 3gp, mp4, etc. I can nearly (image and sound are not sync) get it with avi (xvid mp3) using media player classic and ffdshow_rev2322_20081114_clsid
But with TCPMP, I can get sound for 3gp and avi, but no video at all. All is ok with a compaq armada e500 (P3 500 mhz + 128Mo and W98SE), so I guess this is not a software nor a video encoding problem. Not enough memory (hard to get 128Mo 66mhz ...) and/or not strong enough CPU ?
A vob won't play fine http://samples.mplayerhq.hu/MPEG2/TITLE01-ANGLE1.VOB
A vcd is fine http://samples.mplayerhq.hu/benchmark/testsui … ixbench_vcd.mpg
by the way : ffmpeg -i <input.avi> -target pal-vcd <output.mpg> works great to "produce" your own mpeg1 with FFmpeg version SVN-r15986

Fun fact : this 507DX (without display panel) uses 10 watt while I am typing this txt with some midi playing and 6 watt when idle on desktop