how best to convert a pdf to a high-res jpg?

[Josef Lowder]

.
What is the best and most efficient way to convert a high-res
2.5-meg pdf to a high-res jpg without losing (too much) image quality? 

I tried the 'convert' utility, but the result is poor quality. 
Perhaps there are convert utility options that that might yield 
a better result, but I don't know what they are or how to use them. 

When I load the target pdf file into gimp and then save it as 
a 300 pixel depth jpg image, the quality is inadequate.  When 
I try it at 600 pixel depth, the image quality is better but even 
with a 3-meg file size the image quality is still not as good as 
the original pdf file and my computer (with only 512-meg of ram) 
seems to nearly choke. 

Any suggestions for a better way to get a better result?