The Ti4600 is still a good card for games, but you will lose out on DX9 and AF/AA.
Chances are you will not be able to upgrade the cpu much on that chipset (I'm still running a 266a in my old board and it only supports up to a 2100+). If it's a Palomino, forget about overclocking that puppy cause it's not going to work well at all. You might get it to 2100 or 2200+ stable.
Chances are you are running PC2100 ram so it's basically upgrade mobo, cpu and ram, or just do a vid card for now and the rest later (unless you want or can afford to do all of that now).
If you do decide to go with an upgrade of mobo, cpu and ram, I would probably say to go for an A64 754 mobo, cpu and at least PC3200 ram or higher since it's the best price point right now since the 939pin setups are still a big high and features such as DDR2 and PCI-Ex are not available, unless you want to go Intel
It's a hard choice because your setup is pretty evenly matched. I will tell you though that I got almost 5000 increase in 3dmark2001SE when I went from my 1900+ to a Barton 2500+ @ 3200+ and new PC3200 ram almost 2 years ago. Alas, my TI4400 vid card will not do DX9, is crap for AA/AF, and doesn't get anything much in 3dmark2003, but it still plays everything I've come across.