150gb is enough ... back in 2004 80gigs HDD was enormous ... you have something on it and you can't speed partition ( i always only had two partitions on my HDDS , one for the Windows Virtual cache file , the other for all stuff) ... or don't partition it , it also depends on the speed of your drive ... since you only partitioned HDD by its speed regions
I worked on a Athlon X4 CPU till 2014 , with 3 hdds 550mb,850mb,80gb had on it DOS\Win3.11\Win98\Winxp\VIsta ... you install DOS 6.11 , then Win3.11 then Win98 , then WinXP in a different folder as named WINXP and then VIsta that will automatically create a Dual Boot Window ... then you edit the Autoexec.bat and add before starting the Vista\Winxp , Dos Navigator or Norton Commander and your set ...
Computer starts, shows boot options, you pick one WinXp or VIsta ... before they start DN or NC will start and you can start DOS games or Boot Win3.11 or Win98 ... if you exit DN\NC, WinXP or VIsta will boot ...
and this set up was with me till 2014 ... till my motherboard Soundcard died and fried the motherboard and had to buy a new motherboard with a CPU ...