A newer card would give you DirectX 9 hardware support. There may
be some games that request that as a minimum requirement. So the
advantage of a new card, may be in allowing a more modern game to
load.
Unfortunately, the benchmarking and tech data sites are not keeping
up with all the cards offered for sale. That makes it pretty hard
to give substantial information for comparison purposes. Still,
here are the sites for what they are worth.
http://www23.tomshardware.com/graphics.html
http://www.techpowerup.com/gpudb/
This is your current card.
Ti 4200 NV25 AGP 64MB DDR 250Mhz 250Mhz 128Bits 4 / 2 / 2 DX8.1, PS1.3, VS1.1
A 7600GS is roughly in the right price range. The cheapest cards don't state
their core clock, and may be using cheaper memory or something. This entry
is for the PCI Express version of card, and the stats for the AGP version
are not listed.
7600GS G73 PCIE 256MB DDR2 400Mhz 800Mhz 128Bits 8 / 12 / 5 DX9.0, PS3.0, VS3.0
Is it worth it ? My *guess* would be no. There may not be enough
improvement here, to waste £100 on it. It is all a question of
whether the resulting system would be CPU limited or GPU limited.
(I'm told, for example, that the latest Microsoft flight simulator,
is CPU limited. Oblivion Elder Scrolls is GPU limited.) You should
save the money, towards a system upgrade. A motherboard with a PCI
Express slot, will allow you to select from more worthy video cards.
Yes, the 7600GS is a better card, but is it "£100 better" ? If the
system is a dead end, in terms of upgrading the CPU, then it may not
be wise to sink any more money in the current system.
Gaming is a money sink, and will eat your money as fast as you can
make it.