hehe.. i feel honored to reply to the first REAL plant tank question...
PJ: yes.. you still need fertilizers... Even though the kitty litter may contain iron, it won't contain the trace elements needed for healthy plant growth.
I would suggest a balanced liquid fert. like Tropica Master Grow, or Seachem flourish, or Kent Freshwater Plants in conjunction with Kent Pro-plant.
I like the Kent products cuz when my nitrates are low, I just add a little bit of the pro-plant to up the nitrates.. whereas the other two products do not contain nitrates in them. However, you can also go with one of the other two products and purchase some potassium nitrate powder at a hydroponics shop... then dose the potassium nitrate whenever your plants need more. Keep in mind that you may not even need the extra nitrates.. it really depends on how heavily you planted your tank, with which plants, and the fish load.
In addition, some root tabs here and there wouldn't hurt.
BTW: thanx Johnny.. =)