I have an IBM laptop (r50e model) and I am looking to upgrade the memory as I only have 256mb of RAM.
I tried the kingston memory search, but I could not find any re50 model on IBM.
However, I guess your question is whether or not DDR2 Ram is backwards compatible with DDR ram? And the answer to this would be no, that is most probably not possible.
However, I am not certain that DDR SDRAM is the RAM you need, since I could not find the model of computer you listed on the kingston memory search, nor could I understand it out from the information you listed.
PC100 256MB(2x128) laptop memory for Tecra 8000/8100/8200 IBM T20/T21/T22 Tested, PC100 64 MB laptop memory (narrow stick) for Tecra 8000/8100/8200 IBM T20/T21.., ELPIDA 1GB (2 X 512MB) PC133 Laptop Memory SODIMM HB52RF648DCA-75B IBM 19K4657, 256MB 2x128MB PC133 SAMSUNG m464s1654dts-l7a MEMORY IBM HP DELL SONY LAPTOP RAM, 256MB 2x128MB PC133 SAMSUNG m464s1654dts-l7a MEMORY IBM HP DELL SONY LAPTOP RAM, 256MB 2x128MB PC133 SAMSUNG m464s1654dts-l7a MEMORY IBM HP DELL SONY LAPTOP RAM, 256MB 2x128MB PC133 SAMSUNG m464s1654dts-l7a MEMORY IBM HP DELL SONY LAPTOP RAM, Infineon 256MB PC2700 DDR-333MHz LAPTOP Memory/RAM HYS64D32020DHL-6-D IBM HP, 128MB PC66 Laptop Memory RAM IBM 390 570 600 600E 770 i1400 14E2 i1450 i1500, 64MB PC66 Laptop Memory RAM IBM 390 570 600 600E 770 i1400 14E2 i1450 i1500 2611, 64MB 2x32MB PC66 Laptop Memory RAM IBM 240 390 570 600 600E 770 i1400 14E2 i1500, IBM Thinkpad Laptop X31 Memory Ram Cover, IBM ThinkPad T43 Laptop 1.86 GHZ 1.0 GB Memory 40 GB HD XPPro SP3 A/C Adapter, NEW 512MB DDR 266MHz PC-2100 CL2.5 SODIMM Laptop Memory IBM Thinkpad R32 R40 , 256MB PC133 IBM Thinkpad Laptop RAM Memory Upgrade SODIMM 144pin FRU 19K4855, IBM PC133 512MB LapTop Notebook SODIMM Memory, 38L2993, 1GB 4X 256MB PC2100 DDR IBM ThinkPad R51 R50 T40 T30 A31 Laptop Memory , 256MB PC100 144 Pin Sodimm Laptop Notebook Memory IBM 33L3070, 256MB PC100 CL2 100Mhz 144 Pin Sodimm kit 2x 128MB Laptop Notebook Memory IBM, NEW Samsung 512MB (2x256MB) PC100 SDRAM IBM Thinkpad T20 X20 A21E Laptop Memory, 2GB (2x1GB) Netlist PC-2700 DDR Laptop RAM Memory Kit 333MHz HP IBM Dell Toshiba, 2GB (2x1GB) PNY PC-2700 DDR Laptop RAM Memory Kit 333MHz Dell HP IBM Acer, 2GB (2x1GB) Generic PC-2700 DDR Laptop RAM Memory Kit 333MHz Dell Acer HP IBM, 512MB PC2-4200 DDR2 Laptop Memory IBM 38L5135 73P3843 RAM, IBM A20 T20 T21 T22 256MB PC100 Laptop Memory Upgrade, 512MB PC2100 Laptop DDR Memory IBM ThinkPad R40 2683 , 2GB (2x1GB) Nanya PC-2700 DDR Laptop RAM Memory Kit 333MHz CL2.5 Dell HP IBM, IBM Lenovo Thinkpad 14.1" T400 4GB 2x2 DDR3 PC3-8500 7 Laptop Memory RAM, 2GB (2x1GB) ProMOS PC-2700 DDR Laptop RAM Memory Kit 333MHz Compaq Toshiba IBM, IBM T43 LAPTOP 1.86 GHz CPU 2 GB DDR MEMORY 40 GB Harddrive + MUCH MORE!!! , Elpida IBM 512MB DDR 266mhz PC2100 SODIMM Laptop RAM Memory Module 200pin NONECC, IBM 19K4655 256MB MEMORY PC133 Mhz Laptop SO DIMM-133 19k4654, IBM Thinkpad A22m 15.0" Laptop Modem/LAN RAM Memory Cover Door OEM Original, Ibm Thinkpad T60 laptop-1.83 intel centrino duo core processor/1 gb ddr 2 memory, IBM ThinkPad A22m Pentium 3 1GHz 256MB Memory DVD-ROM 14" Laptop - Loads BIOS, 256MB PC2100 DDR 266 Laptop Memory RAM For HP DELL IBM, 256MB 256 MEG RAM MEMORY UPGRADE IBM LENOVO THINKPAD A20/A22/T20/X20/X21 LAPTOP!, IBM 32mb SDRAM DIMM-66 Laptop RAM Memory FRU 10L1226 (from Thinkpad 390), LOT 4pcs OF EDO SODIMM LAPTOP MEMORY RAM DRAM 144pin DELL IBM+, 512MB laptop notebook 667MHz PC2-5300S RAM memory Dell D420 D430 etc IBM Acer HP, IBM Thinkpad T42 Laptop/Notebook with CPU & Memory Upgrades + Docking Station, Samsung 128 MB, memory module laptop, IBM FRU 20L0265, IBM 128 MB, PC133, memory module laptop, IBM FRU 19K4653, 1GB DDR2 PC2-4200 200pin Laptop Memory DELL HP IBM -30 DAY $ BACK WARRANTY!, IBM Thinkpad R51 Laptop Memory Cover 91P9813 , IBM Thinkpad R51 Laptop Memory Cover 91P9813 , IBM ThinkPad A31 A31P Laptop Memory Door Cover , IBM ThinkPad A30 A30P Laptop Memory Door Cover 26P9460, IBM 2GB DDR2-533 PC2-4200 Laptop SODIMM Memory Module 73P3847, IBM Thinkpad A21m LAPTOP MEMORY COVER ,