How do I find out more information about ext3 or ext2 file system?

You need to use a command called dumpe2fs. It displays lots of useful information about your ext2 or ext3 file system. General syntax is as follows:
dumpe2fs /dev/device

It displays following type of information:

1. Filesystem volume name
2. Last mounted on
3. Filesystem features: has_journal ext_attr filetype needs_recovery sparse_super
4. Default mount options
5. Filesystem state
6. Filesystem OS type
7. Information about blocks etc

For example, display information about /dev/hdb1

$ dumpe2fs /dev/hdb1

Output:

Filesystem volume name:   /
Last mounted on:          
Filesystem UUID:          7a965fb9-bf9e-4ed5-8a01-321386b843d9
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr filetype needs_recovery sparse_super
Default mount options:    (none)
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              2443200
Block count:              4883752
Reserved block count:     244187
Free blocks:              677028
Free inodes:              2063116
First block:              0
Block size:               4096
Fragment size:            4096
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         16288
Inode blocks per group:   509
Last mount time:          Thu Mar 16 23:25:43 2006
Last write time:          Thu Mar 16 23:25:43 2006
Mount count:              20
Maximum mount count:      30
Last checked:             Sun Mar 12 01:16:43 2006
Check interval:           0 ()
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:               128
Journal inode:            8
First orphan inode:       782426
Journal backup:           inode blocks
Group 0: (Blocks 0-32767)
 Primary superblock at 0, Group descriptors at 1-2
 Block bitmap at 3 (+3), Inode bitmap at 4 (+4)
 Inode table at 5-513 (+5)
 93 free blocks, 15966 free inodes, 8 directories
 Free blocks: 8844-8855, 9099-9126, 9129-9137, 9139-9142, 9146-9151, 9154-9155, 9158-9165, 9170, 9172, 9174-9176, 9178-9179
, 9182-9189, 9191, 9193, 9196-9197, 9200-9204
 Free inodes: 114, 126-164, 172, 362-547, 549-589, 591-16288
Group 1: (Blocks 32768-65535)
 Backup superblock at 32768, Group descriptors at 32769-32770
 Block bitmap at 32771 (+3), Inode bitmap at 32772 (+4)
 Inode table at 32773-33281 (+5)
 6250 free blocks, 13747 free inodes, 143 directories
 Free blocks: 38912-38919, 56874-57138, 57141-57343,
....
.....
.