Well, after researching a dozen more sites, I finally found one with an answer... Looks like this is not a new problem, but few answers had been given so far... Thought I'd share it in here, in case someone else is having the same problem...
So, here's the solution that worked for me:
1. At the first Mandrake screen, type F1.
2. At the command prompt that follows, type "linux mem=512M"
3. The installation starts!
Good day for everybody!