I know Pentium 4 with 512 MB ram may sound ancient but many people (specially students) still use these machines . Right now many people a stuck with Windows XP .
It doesn’t just sound ancient, it is in fact ancient. Almost all Pentium 4 cpus are both 32-bit and single-core. There have been mainstream dual and quad core 64-bit cpus for over ten years. = Also Windows XP came out in 2001 (18 years ago). And my old desktop from 2004 (an off the shelf compaq) came with 512MB standard.
Also while I think for someone in that position XP might be more usable, any 32-bit Linux will be more modern and run okay for the most part though 512MB ram would be rather tight in a lot of cases.
You may as well try the nightly. Since the whole OS is beta at best and I don’t think there’s really any total upgrade mechanism, you may as well try the latest.
The LiveCD runs fine on my Pentium 4 machine (which has full Linux Mint install on the HD),though I have 4 GB of ram. I did have some initial problems with booting Haiku that I think were related to initializing the graphics card. The Haiku boot options though allowed me to get around that at least as far as booting and basic functionality. You will probably find that the basic stuff works okay, but some things may cause your system to choke, like web browsing or trying to stream media.
I would like to second the suggestion above that you upgrade to at least 1 GB. At the low end of RAM amounts, anything you can add usually is a significant improvement. If possibly I would advise at least 2 GB though as that would be a lot more pleasant under any modern OS.