32/64 bit, depends upon you. If you have 4GB + ram and you want to utilize it fully in Ubuntu as well, then go for 64bit else stick to 32bit.
You said the screen freezes during installation. Try booting the liveCD wtih "acpi=off" option.
Well you need to understand linux directory and partitions properly. /dev/sdxy is the drive partition where x is to be replaced by drive letter and y by the partition number.
Sometime, partitions may be seen as /dev/hdxy , but the case is almost same.
/dev/sda is your mbr and /dev/sda1, /dev/sda2/ etc are your partitions no matter they are EXT,FAT or NTFS etc. To understand linux directory stucture ,see
here.
For partitioning details see
this page.