pc133 or ddr 2100

hi,
i'm making a P4 Northwood computer with my left over old parts.
my mobo can take both sdr pc133 ddr 2100;
i have 1gig of pc133 and 512 meg of ddr2100.
it's sad that mobo cannot combine sdr and ddr;
which one should be better?
1gig pc133 or 512meg ddr2100
this computer is for kids; so it will be used for every thing
i.e. surfing the web, games, media play, etc.

spec:
2.53ghz p4 northwood
unknown msi oem m-atx mobo
geforce 6600gt agp 128mb
creative sb audigy ls
4x 40gig hdd ata100 & 133 mixed for raid 0
1gig pc133 or 512meg ddr2100
noname brand 400W ps

Go for the biggest RAM capacity: latency is exactly the same, only bandwidth increases, but if you don't do much video editing or multimedia encoding you'll not notice any difference in speed.
Windows loves awfully big amounts of RAM.