What’s the difference between quad core processors and IntelCore i3, i5 & i7′s ?

I am look at buying a laptop, and do not understand the processors you can buy. It has been recommened that i get a quad core processor as i need it for architecture software, however the one i am looking at buying has an intel core i3 processor. Are the quad core’s better, worse or indiffrent to the intel i3? Can someone explain in simple terms for me?

I would suggest to buy i5 processor laptop
1)Dell Inspiron i1764-6075OBK 1764 17.3-Inch Laptop (Obsidian Black)
*2.26GHz Intel Core i5-430M Dual Core Processor (2.53GHz Turbo Mode, 3MB Cache)
*4GB System Memory; Media Card Reader; 10/100 Ethernet; Wireless-N Mini-Card
*500GB Hard Drive; 8X Dual Layer DVD+/-RW Optical Drive
*17.3″ HD Display; Integrated Intel Graphics Media Accelerator HD; 1.3MP Webcam
*Windows 7 Home Premium Operating System (64-bit); 6-cell Battery

http://www.amazon.com/Dell-Inspiron-i1764-6075OBK-17-3-Inch-Obsidian/dp/B0030T17GO/?tag=bdd-linking-001-20

2)ASUS Republic of Gamers G73JH-A2 17-Inch Gaming Laptop (Black)
*1.6GHz Intel i7-720QM Quad-Core Processor
*8GB DDR3 1066MHz; 4 SODIMM Sockets; up to 8GB
*1TB (500G 7200RPM x2) HDD; Super-Multi DVD Drive; 802.11 b/g/n
*17.3-Inch Full HD LED Display; ATI 5870 Graphics with 1G GDDR5; 2.0M Webcam
*Windows Home Premium 64-bit Operating System; Gaming Backpack and Mouse Included

http://www.amazon.com/Republic-Gamers-G73JH-A2-17-Inch-Gaming/dp/B0036ZE6SS/?tag=bdd-linking-001-20

3)Toshiba Satellite A505-S6030 TruBrite 16.0-Inch Laptop (Black/Silver)
*2.8GHz Intel Core i7-720QM Processor
*4GB 204-Pin DDR3 SO-DIMM Memory
*500GB Serial ATA Hard Disk Drive (5400RPM); DVD SuperMulti Drive with Labelflash
*16″ CCFL (16:9) 1366×768 Display; NVIDIA GeForce 310M Graphics
*Window 7 Home Premium 64-bit

http://www.amazon.com/Toshiba-Satellite-A505-S6030-TruBrite-16-0-Inch/dp/B00313JXMO/?tag=bdd-linking-001-20

Try to search here you can find more options :

http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=laptop+i5&x=0&y=0&tag=bdd-linking-001-20

Toshiba Portégé R700 Powerful Ultra Portable Hands on