Hacking G6 lite storage problem

[Lynk]

i just got my hands on a g6 lite yesterday and first problem i noticed no matter
wot i tryed (formatting fat16 + MPUtility) as suggested in many posts my g6
firmwire will not update but the thing that is getting really annoying atm
is altho after running many checks and the card coming up fine i cannot
use more then 100mb out of the 500mb available without the card crashing
in the writer, now i dont think the card is corrupt as the games play fine
on ds and saving works great.

any ideas or suggestions much appreciated thanks