[plt-scheme] Memory problem on Mac OS

I was executing the program tie-dyed from section 11.3.2 of HTDP and I
received an error message in a new window that said "Out of Memory!" and
gave one button option, Quit.

I am working on a Mac G4 running Mac OS 9.2.2 with version 204 of DrScheme.
I have allocated 31000k to the application and my RAM is 512 MB. I am not
running any other applications at the time, I have a lot of hard disk space
and Virtual Memory is turned off. I was running with Virtual Memory on and
it gave me this message, so I turned it off and restarted and it still gave
me the above message.

I also had this problem when I was first starting with drawing on a canvas
from earlier in HTDP. I simply increased the memory a lot and it worked. But
I am wondering if DrScheme is one of those applications that doesn't like
too much memory. If so, then what do I do for increasing the memory when I
get this message? It is extremely frustrating, but I have learned to save
after every line of code I type.