DTMF signal generation on ML507 board (Virtex 5 FPGA)

Hi,
For a school project I need to design a signal generator which generates digital touch-tone-signals (DTMF) with duration of 60-70 ms that can be used in DTMF-telephony. the signals later will be fed to the on-board existing Digital-to-Analog converter and then to the exisiting on-board AC97 audio codec.
I have spent long hours on researching after implementation ideas but I am still very confused about the right direction.
I know I need to generate overall 8 different frequencies and each DTMF tone must contain one sinusoid from the high- frequency group (1209, 1336, 1477 and 1633 Hz) and one sinusoid from the low frequency group (697, 770, 852 and 941 Hz).
How do I design it with VHDL code? should I use the principle of NCO (numerically controlled Oscillator) and use LUT for each frequency? if so, what size of LUT should I create? 20 samples dhould be enough? is there a better approach to implement this?
I would very much appreciate any idea or an hint or even better, VHDL code which could help me out here.

Thank you in advance,

Once i did this but i remember i use a control loop that was marginally stable, so then i had to just change some parameters so that the oscillation frequency where the DTMF ones.

If you want to know how many point sdo you need, you should try matlab first, check this with a real telephone putting the mic on the computer speaker. Once you got a design that works, go to HDL. Maybe this could work with a triangular signal, or even better with a clk signal(train-pulse), but you need to try this first.