451 cheap 4X DVDR write unstable

My config is Nero 6310+Incd4121
WinXP, P3-733, 314MbRam
(1) I have some cheap 4X DVDR+ disk (SKY 4XDVDR+ AML code), if it is write at 2.4X, it must be readable (100% ok). If it is write at 4X, PIPO is higher at 20% of capacity and at the end, this is good case. But sometimes the disk is unreadable, 451 can’t write the TOC totally. Since this reason, I only try this disk @2.4X. Any good suggestion.
(2) my dvd writer is 2nd IDE master, and an ASUS 45X CDROM as slave using 80pin ide cable. I find that if 2 drive are access at sametime, 451 running Kprobe and Asus is reading vcd. it is signal noise as Kprobe read error and Vcd can be play, what is the problem.
(3) After dvd/cdr wrote, i need to reject it and load again to read it, but my office’s cdr writer can refresh the disk immediately, how can I solve this one, as sometimes I need to try twice to read a DVDR just finish writing…