An Antec 450-500watt PSU will have better power management, providing you with more available power; rather than a cheap 600watt own-brand PSU; which often will output roughly half of what it claims it can.
Also as far as the HDD goes, it all depends on what you use your PC for. I currently have 3x 320GB with a futher 500GB on an external USB HDD. Although I do only have the external drive purely for Video Editing means; the internal drives are all almost completely full. (have around 45GB left)
Reason I have so little is partly because of the software I have installed:
Windows Vista Service Pack 1 - 25GB
Microsoft Office 2007 - 2.8GB
Microsoft Expression Studio 2 - 1.5GB
Microsoft Visual Studio 2005 Professional - 2.4GB
Microsoft Xbox 360 Software Development Kit - 3.5GB
Microsoft DirectX Software Development Kit - 1.5GB
Havok Physics (Full) Software Development Kit - 1.0GB
PhysX Physics (Full) Software Dvelopment Kit - 0.6GB
Adobe Creative Studio 3 Extended - 3.5GB
Autodesk Maya 8.5, Sketchbook 2009, MotionBuilder 2009 - 3.0GB
Gears of War - 10GB
Unreal Tournament 3 - 8.5GB
Civilization IV (Warlords + Beyond the Sword) - 3.8GB
Final Fantasy XI 2008 Edition - 15.2GB
Cold Fear - 3.2GB
Silent Hill 3 - 3.8GB
The Sims 2 (All additional content packs) - 21GB
Tomb Raider Legend (+ Anniversary Expansion) - 14GB
Dawn of War (+Winter Assault, Dark Crusade & SoulStorm) - 16GB
Jade Empire - 8GB
Knights of the Old Republic 1 & 2 - 13GB
Half-Life 2 (+Episode 1, 2, Portal, CS: Source, DoD: Source & Team Fortress 2) - 31GB
EVE Online - 4GB
Guild Wars (+Nightfall, Factions & Eye of the North) - 3.4GB
(I probably have a few more things installed knowing my brother but that's what I can recall off-hand)
but also I store a good number of my DVD and Movie Collection on one of my hard disks (so that I can just stream to my consoles), plus I've taken to using iTunes/NetFlix/Microsoft Music for purchasing new stuff.
I mean when you think about the fact a single album generally takes up around 500MB, it's not much when you have one; but when you have a few then it starts eating space quickly.
Same with movies, in SD you're looking at around 1.5-3GB when you do a convert-burn using Media Player to WMV11. The HD formats can be as large as 12GB each... and that's if I'm just storing the film itself not any of the DVD special features (which often I will cause some are quite good).
I also get a great many games via digital purchase (i.e. Steam), as well as storing many of my older game CD/DVDs on my HDD so that my discs can be kept safe somewhere else given how difficult some titles are now to get ahold of.
Lastly I keep a regular "backup" of software and past projects on one of the Hard Disks. I have literally filled 320GB with work media, concept artwork, sdks, etc..
Really boils down to what you're using your system for; but for modern systems; 80GB is nothing. 250GB is really a minimum requirement imo