Hey Diddy, thanks for that. In the meantime, I've found out that your thoughts were correct, you can only have 1gig in each slot. The only exception is if the memory is Aeneon. I'm quite suprised it accepted it at all. When you find your replacement, they should be 1gig DDR2, PC2-3200 or PC2-4300, Unbuffered, Non-ECC. Here is a compatibility list for that motherboard:
Size Vendor Model Brand Side(s) Component A* B*
256MB Kingston KVR533D2N4/256 Elpida SS E5116AB-5C-E
256MB Kingston KVR533D2N4/256 Elpida SS E5116AF-5C-E
512MB Kingston KVR533D2N4/512 Hynix DS HY5PS56821
512MB Kingston KVR533D2N4/512 Infineon SS HYB18T512800AF3733336550
1G Kingston KVR533D2N4/1G Kingston DS D6408TE7BL-37
1G Kingston KVR533D2N4/1G Micron DS 5YD11D9GCT
256MB Samsung M378T3253FG0-CD5 Samsung SS K4T56083QF-GCD5
512MB Samsung M378T6553BG0-CD5 Samsung SS K4T51083QB-GCD5
256MB Infineon HYS64T32000HU-3.7-A Infineon SS HYB18T512160AF-3.7AFSS31270
512MB Infineon HYS64T64000GU-3.7-A Infineon SS HYB18T512800AC37SSS11511
512MB Infineon HYS64T64000HU-3.7-A Infineon SS HYB18T512800AF37FSS29334
512MB Infineon HYS64T64000HU-3.7-A Infineon SS HYB18T512800AF37SSS12079
512MB Micron MT 16HTF6464AG-53EB2 Micron DS D9BOM
512MB Micron MT 16HTF6464AG-53EB2 Micron DS Z9BQT
1G Micron MT 16HTF12864AY-53EA1 Micron DS D9CRZ
512MB Corsair VS512MB533D2 Corsair DS MIII0052532M8CEC
512MB Elpida EBE51UD8ABFA-5C-E Elpida SS E5108AB-5C-E
512MB Kingmax KLBC28F-A8KB4 Kingmax SS KKEA88B4IAK-37
256MB Kingmax KLBB68F-36EP4 Elpida SS E5116AB-5C-E
512MB Kingmax KLBC28F-A8EB4 Elpida SS E5108AE-5C-E
512MB PQI MEAB-323LA PQI SS D2-E04180W025
1G PQI MEAB-423LA PQI DS D2-E04230W107
512MB AENEON AET660UD00-370A98Z AENEON SS AET93F370A G 0513
256MB AENEON AET560UD00-370A98Z AENEON SS AET94F370AWVV34635G0520
512MB AENEON AET660UD00-370A98Z AENEON SS AET93F370A 3VV36328G 0522
512MB AENEON AET660UD00-370A98X AENEON SS AET93F370A 0518
512MB AENEON AET660UD00-370A88S AENEON DS AET82F370A 0550
1G AENEON AET760UD00-370A98Z AENEON DS AET93F370A 0551
2G AENEON AET860UD00-370A08X AENEON DS AET03F370AFVV26176G 0542