I found this by accident...
when prompted to partition answer with this: /dev/mmcblk0p1: 0,999999,6
It will reply back that 999999 exceeds the maximum and your maximum is xxxxx. You then have another try to set the first (fat) partition.
Subtract the size you need/want from what you have available and replace the 999999 with that value.

*Use 9999999 if you have a 1TB card who knows maybe someone 8 years from now looks at the thread.

Now, what we really need is a good guide on setting partition sizes. Since the N800 and N810 come with 256 (i think), then 400 or 500 is plenty. If you plan on installing KDE, you will need 2300 (i think is the current suggested size). I see Open Office is installable and needs 1300 and maybe another 500 for swap file space. I think even the larger 'normal apps' like Canola and GCompri max somewhere under 100 with all the plugins. This also assumes you don't have a lot of document files or they are stored on the first/fat/accessible from PC partition. Are they assessed any faster on the linux partition?

PPS. Some of the guides say to make the first partition ,0C some say ,6. It mostly doesn't matter since they get reformatted latter in the process, but which is more correct?