I've got a g4 and DP and a nice new roland VX3080 module which I thought would do the job because you can add expansion cards.
BUT!!! - I still don't think the sounds are good, It's clear that Roland could do a better job with their tones but go for quantity rather than quality.
i have their best cards and I still don't have a good flute or oboe or horn or clarinet.
I looked into getting patches(or tones, sounds) off the web like with Gigasampler but it's not for the MAC. Does anybody know how I can use 3rd party sounds (patches or tones) with DP or pro tools. I have both.

If you are looking for samples... you could try http://www.samplenet.co.uk/ and search for the type of sounds you are looking for. They are all free samples and have a nice selection. You can download them but they will either come as .mp3 or .wav form and you will just have to convert to .aiff unless DP accepts wav or mp3 files.

Other than that, you could purchase a CD filled with orchestral instruments and use them as needed. I know that Jordan R. from Dream Theater does that but he uses a nice sampling keyboard. It just depends on how you plan to use the sounds.