I don't think anybody can help you with the details supplied.
1. Which Windows?
2. Video from what camera in what format?
3. Project settings?
4. How was it captured, what codec?
5. Disk setup?
6. Video card and driver version?
7. What did you try to solve the issue?
8. Can you replicate it on another PC?
1. Windows XP Pro SP3
2. Canon XM2, DV format
3. DV PAL, 48kHz, standart
4. It was captured with the same Premiere CS4
6. Integrated Intel 82910/915GL with newest drivers (updated with Intel Driver Update Utility)
7. Tried to install different codecs, reinstalled Windows about 5 or 6 times, downloaded all updates for hardware, windows and adobe.
8.I installed a trial of Premiere CS4 on another computer. It works fine with same settings and same camera.
With that marial and those project settings you should not see a red line. It does not require rendering.
Can you try with a different video card. Integrated video cards are lousy performers. What is your disk setup? Single disk, more than one? What connections, USB, firewire, SATA, eSATA? Any partitioning on the disk(s)? What other processes are running? Virus protection, spyware and the like?
When I get other video card wtih low profile bracket I will try (Computer is HP Desktop). Disk is WD SATA 80GB. Partitioned: C:\ 60GB D:\ 20GB Only Avast! Antivirus is working. The strangest thing is that before reinstall it worked fine. Maybe something additional must be installed...
At least remove the partition, it only slows things down. Remove Avast, that slows things down even further. Get at least one or two additional disks for media. Check other processes.