it is really necessary to format the hard drive in EXT3+swap ?
Everything depends on you
However, if you're going to use BT, or ed2k or other p2p software --- you need swap. If you're going to install extra packages through ipkg system you need at least ext3 (or 2) partition, because fat32 doesn't support symlinks and file permissions, and ntfs is supported only read-only. You can keep your data either on ext3, or fat32 partitions (doesn't matter), but fat32 has 2 Gb filesize limit... the rest is your choice ))