Hello NVonShats and welcome to the forum! Glad to have you. You made a wise choice picking the eXpo and then coming here to learn how to make it as good as it can be.
Will these upgrades harm my phone in any way ... (referring to Tweaker and this special ROM that Dark made)
Both the Expo/IQ Tweaker and any custom ROM (not just Dark's Dragonstorm series) make changes to either the Windows Mobile registry and/or the files and file structure of WinMo itself on your phone. So, the short answer is:
Possibly, But Not Likely. Tweaks and custom roms CAN harm your phone if 1: they are installed improperly (aka: always follow all directions) or 2: they are poorly written to begin with (not a problem here). The good thing is, you can always restore your phone back to it's original condition. Unless, of course, you get into a hot tub with it in your pocket - there's no coming back from that

what is a tewaker and what will it do for m phone?
Click on the link for Woodhole's Tweaker in my signature - it won't start downloading, but will take you to the thread where what all it does and how to use it is discussed in depth.
is the Rom worth it?
Most smartphone are virtually crippled by the limitations the wireless carriers put on them, and the unrealized potential of most smartphones is hidden by manufacturers that err on the side of being cautious and over-conservative.
Leaving your eXpo "stock" is the equivalent of using a Formula 1 car to pull a cement mixer and never getting it up over 55 mph.
i really need to upgade my computer to Windows7 for me to get the best for my phone?
XP or Windows 7 are recommended for interfacing with Windows Mobile - Vista just has too many driver and compatibility issues for me to recommend it (even though that's what I'm stuck with currently) and ROM flashing won't work reliably or at all on Vista.
Hope that helps!
RC