OK from the start let me say I am a computer tech with 14 years industry experience. I have built literally thousands of computers in that time both as part of my business as well as working in a couple of Qld schools as an IT Tech.
Win 7 Pro is a waste of time and money unless you are in a multi PC Network or using it as a business computer, again on a network - Win 7 Home is more than adequate for all home users need. The only reason Pro is good is the added networking capacity.
DVD burners, printers, scanners all will work on a 64bit system without any problems as 64 systems can also run 32 bit programs (but not the other way around - you can't run a 64 bit program on a 32 bit system)
RAM - minimum I would be looking at without a dedicate video card would be 4Gb, with a video card I would look at probably 8Gb with a 1Gb video card. (They will work on both 32 and 64bit systems).
You can actually slow a system down by installing too much ram - so check your motherboard specs first.
Monitor, sound system, keyboard, mouse won't be effected by a change in 32bit to 64 bit.
How to pick your new components
1) Motherboiard - Intel or AMD? What do you want it for? Onboard graphics or seperate video card, How many USB ports, do you need to have a RAID array or just a couple of hard drives.
2) CPU - are you looking at a gaming machine, graphics intensive or just a run of the mill PC?
3) RAM? What type and how much will you need? I have run a windows 7 install on 256Mb, it ran like a one legged dog but it ran.
4) Are you going to build it yourself or just buy off the shelf?
5) where are you looking at?
Umart has an online parts picker - : http://www.umart.com.au/newindex2.phtml?bid=4
Have a look at this for a basic system:Motherboard
: Gigabyte GA-Z77MX-D3H MB, Intel Z77 Chipset, Socket 1155, 4x DDR, SATA3, USB3.0, GbELAN, 7.1CH Internet Price: $119.00 (Supports up to 32Gb DDR 3 RAM)CPU
: Intel Core i3 2130 3.40Ghz 3MB Cache LGA1155 CPU Internet Price: $145.00 RAM
: Kingmax 8G(1X8G)PC-10600 1333MHZ DDR3 Internet Price: $42.00Operating System
Microsoft Windows 7 Home Premium 64bit OEM(Microsoft OEM Terms&condition apply)
Internet Price: $93.00 (I would also get a hold of the latest Ubuntu - free OS and dual boot it) Videocard
: Gigabyte GF GT610 Silent PCI-E 2.0 1GB 64-bit DDR3,810/1200 MHz,DVI,HDMI,VGA,Fan,LOW PRO Internet Price : $41.00 Case
: Thermaltake Black Versa II Mid Tower Chassis & 500w PSU (USB3) Internet Price: $73.00 Hard Drive
: Seagate SATA3 1TB 7200RPM 64mb Cache Internet Price: $78.00 DVD/Blueray Burner
: LG BH14NS40 BLK BluRay Burner OEM Burner,10xBD-R Read/Write, 16xDVD+-R Read/Write,SATA, Silt Play, Win7Comp
Internet Price: $89.00 Total $638.00
(if I added it up right. Very similar to my system (Motherboard, RAM, CPU all the same but I have 3 1Tb hard drives and a dedicated 1Gb video Card and a few other tweaks)
You can even get Umart to build the system for you and get it all delivered in one piece if you don't want to build it yourself.