Rebuild PC or buy new? Laptop or Desktop?

I have a desktop PC purchased in 2004. It has the specs posted below. I installed a new DVD burner which works if I could get it to open. I have also installed a 2nd hard drive (931 gb?). I added a firewire port to download my mini DV camera movies. I have re-installed Windows XP on it but would like to put Windows 7 on it. I wonder if it is too old to do this with or if something on it isn't high powered enough to handle it. Should I put in a new motherboard? A new fan? As to what I do on my computer: I watch a lot of online TV such as Hulu,
Dimension 4700
Pentium® 4 Processor 530 with HT Technology (3.00GHz, 800 FSB), Microsoft® Windows® XP Home Edition
Dell Dimension 4700 Series Pentium® 4 Processor 530 with HT Technology (3.00GHz, 800 FSB)
Memory 1GB Dual Channel DDR2 SDRAM at 400MHz (2x512M)
1GB4P

Video Cards 128MB PCI Express™ x16 (DVI/VGA/TV-out) ATI Radeon™ X300 SE
Hard Drive 80GB Serial ATA Hard Drive (7200RPM)
80S
Floppy Drive and Additional Storage Devices 3.5 in Floppy Drive
FD
Operating System Microsoft® Windows® XP Home Edition

Network Interface Integrated Intel® PRO 10/100 Ethernet
IN


CD or DVD Drive Dual Drives: 16x DVD-ROM Drive + 48x CD-RW Drive
DVDCDR

Sound Card Sound Blaster® Live! 24-bit ADVANCED HD™ Audio

Speakers No Speaker Option
N


Digital Music Dell Jukebox - easy-to-use music player and CD burning software
MMBASE
[412-0691]
Digital Photography Paint Shop™ Pro® Trial plus Photo Album™ Starter Edition
DPS

Dell Media Experience Dell Media Experience
DMX