Minecraft lag baucoup alors que j'ai des bonne config pc

Bonjour,

Je joue a minecraft depuis la version 1.2.5 est depuis toujours il lag énormément je dois mettre la vision en mini sinon sa ne vas pas. J'ai pourtant un bon pc :

MS Windows XP Home 32-bit SP3
Possesseur AMD Athlon 64 3000+ 2Ghz
1.5GB de ram DDR1
carte mère ASUSTek Computer INC Salmon 03q0211RE101SALMO00
carte graphique GeForce 6200 512MB Résolution 1280 par 1024

J'ai eu aussi récemment ce crash report alors que jouai sur mon serveur en locahost avec bukkit 1.4.2 r1

---- Minecraft Crash Report ----
// Why did you do that?

Time: 03/11/12 18:03
Description: Exception in server tick loop

java.lang.OutOfMemoryError: Java heap space
at yy.<init>(SourceFile:9)
at zb.<init>(SourceFile:24)
at zx.d(SourceFile:80)
at id.c(SourceFile:78)
at id.d(SourceFile:100)
at xe.e(SourceFile:260)
at xe.a(SourceFile:203)
at xe.c(SourceFile:216)
at xe.b(SourceFile:191)
at zr.a(SourceFile:58)
at ie.b(SourceFile:502)
at ie.a(SourceFile:471)
at xe.<init>(SourceFile:162)
at ie.<init>(SourceFile:64)
at bcb.a(SourceFile:70)
at bcb.c(SourceFile:99)
at net.minecraft.server.MinecraftServer.run(SourceFile:570)
at fp.run(SourceFile:818)

Relevant Details:
- Minecraft Version: 1.4.2
- Operating System: Windows XP (x86) version 5.1
- Java Version: 1.7.0_09, Oracle Corporation
- Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Oracle Corporation
- Memory: 8912904 bytes (8 MB) / 259522560 bytes (247 MB) up to 259522560 bytes (247 MB)
- JVM Flags: 0 total;
- AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
- Is Modded: Very likely
- Profiler Position: N/A (disabled)
- Player Count: 0 / 8; []
- Type: Integrated Server