Yes, I did find a solution.
Check out this facebook album
The album is viewable as long as you got a facebook account.
There's a hidden 44-pin 2,5" ide port on the motherboard, under a blue DiskOnModule PCB board.
By using this, I could install win xp, and actually surf the internet, etc with wifi usb dongle, etc etc. The most I could do in multitasks was listening to internet radio, surf the web (non-flash sites) and copy 3-4 folders at the same time, before it started lagging abit. Quite good if u ask me. Also used this guide to make windows xp faster with my Thin Client:
Also, this site got tons of info on Compaq Thin Clients: (link to ur model) newbielink:http://www.parkytowers.me.uk/thin/hp/t5520/index.shtml [nonactive]
U see the blue pcb on the left top side of the motherboard picture
Edit: Tried to fix the links 3 times, but doesnt seem like it want to