Shortage of memory will slow it down, but not usually that dramatically.
There's an easy way to find out: it's worth trying this -
Click Start - Run
Type in the box the one word msconfig
Click the "Startup" tab that appears.
Untick everything (it'll stay there, so you can re-tick it later if need be).
Click "Apply"
OK your way out and restart the machine.
It will warn you about having turned stuff off - leave it off until it's rebooted fully, and see how much faster that was.
If it's still slow, that wasn't the problem and you can re-tick everything.
If it now starts quickly, then try turning stuff on one or two at a time till you find those that really slow things down. Are they packages you actually need running in the background all the time?