lian li 800 desktop case power supply issues

ok, I haven't had a desktop PC since my old pentium 150! I just completed my system using a beautifully constructed lian li case that has the power supply INSIDE in front. i am using an old 450 watt thermaltake at the moment, but I know this isn't the best solution. What if any suggestions for this case would you guys recommend.
I am using the onboard video at the moment, because the old fan strapped to the butt of this power supply is poking into the case too far to install all but the most extreme short cards. Also of importance, the way the case is designed, it does have issues with my old power supply pushing air out when the case design sheet shows air flow going the other direction.

lian-li 800B case, MB amd690gm-m2, 1 gig corsair, 4600+, eventually2 sata disk drives... 1 dvdrw light scribe on order. currently using an older TDK ide dvdrw, 2 wd 7200rpm sata2 HDD, usb card reader floppy combo that has really done much better than I'd hoped, flat panel widescreen 19inch aoc monitor, older pci tv card.