Dell :: 600m Memory Upgrade

My hdd crapped out and I'm replacing it - I am toying with the idea of upping my memory as well. Current memory:

DUAL IN-LINE MEMORY MODULE, 256, 333, 32X64, 8K, 200

I am looking at one stick of:

Transcend 1GB 200-Pin DDR SO-DIMM DDR 266 (PC 2100) Notebook Memory Model TS128MSD64V6A - Retail

I mainly use office and surf the net.
PROCESSOR, 80535, 1.5G, 1M, PENTIUM M BANIAS, PLASTIC GRID ARRAY, INSPIRON

1) Given my usage and proc, is adding 1gb overkill?

2) Is there any advantage to getting 2 new sticks of 512, rather than one new stick of 1gb and 1 old stick of 128mb?

3) Is there any advantage to getting higher-speed ram (PC>2100)?